Use the standard half-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.) 3 Cl2(g) + 2 Fe(s) → 6 Cl-(aq) + 2 Fe3+(aq) Cl2(g) + 2 e- → 2 Cl-(aq) E° = +1.36 V Fe3+(aq) + 3 e- → Fe(s) E° = -0.04 V

Answers

Answer 1

The cell potential for the electrochemical cell has been 1.40 V.

The standard reaction for the cell will be:

[tex]\rm 3\;Cl_2\;+\;2\;Fe\;\rightarrow\;6\;Cl^-\;+\;2\;Fe^3^+[/tex]

The half-reaction of the cells has been:

[tex]\rm Fe^3^+\;+\;3\;e^-\;\rightarrow\;Fe[/tex]

The potential for this reduction has been -0.04 V.

[tex]\rm Cl_2\;+\;2\;e^-\;\rightarrow\;2\;Cl^-[/tex]

The potential for the reduction has been 1.36 V.

The cell potential has been: Potential of reduction - Potential of oxidation

Cell potential = 1.36 - (-0.04) V

Cell potential = 1.40 V.

The cell potential for the electrochemical cell has been 1.40 V.

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Related Questions

A runner can cover 2.0 miles in 31 minutes, how long would it take for this runner to cover 6.0 Km. Hint (1 mile= 1.609 Km)

Answers

The answer to this question is approximately equal to 57.8

what is the lewis structure for OP(N3)3​

Answers

Explanation:

this is the ans

hope this helps

What is buffers and mention its importance?

Answers

Answer:

Buffer is the chemical substance that addition of acids and bases, maintaining constant environment,its called Buffer.

Explanation:

Buffers are use in the system to maintain the value of pH, and the contain the pH value is not to change.Buffer maintain the body of pH for the optimal activity,and they are solution of pH constant.Buffer in used in the lab and that to maintain growth of the micro tissues and the culture media.Buffer are used in maintain necessary optimal reaction activity,determine the indicator of solution with pH.Buffer capacity is that concentration to the buffering agent, is the very small increase,buffer capacity to the pH is 32% , of the maximum value of pH.Buffers in a acid regions to the desired of that value to the particular buffer agent.Buffers can be made from that a mixture of the base and acid, buffer can be a wide range of the obtained.Buffers that the pH  calculation and they required to performed in the critic acid that the overlap over the buffer range.

Which of the following goes through the largest volumetric change? Question 4 options: A) Water when it's heated from 1oC to 99oC B) Water when it freezes into ice C) Ice when it melts into water D) Water when it boils into steam

Answers

Answer:

Water when it freezes into ice

Explanation:

Most liquids expand when heated and contract when cooled, water behaves in an anomalous fashion. Water rather expands when cooled and contracts when heated.

Water usually contracts on cooling from any temperature until 4°C, after 4°C, the water begins to expand rapidly. Hence water has its least volume at 4°C and increases rapidly afterwards.

Thus the largest volume change for water occurs during freezing since it expands when cooled.

The equation represents the decomposition of a generic diatomic element in its standard state. 12X2(g)⟶X(g) Assume that the standard molar Gibbs energy of formation of X(g) is 4.25 kJ·mol−1 at 2000. K and −63.12 kJ·mol−1 at 3000. K. Determine the value of K (the thermodynamic equilibrium constant) at each temperature.

Answers

Answer:

[tex]K^{2000K}=0.774\\\\K^{3000K}=12.56[/tex]

Explanation:

Hello,

In this case, considering the reaction, we can compute the Gibbs free energy of reaction at each temperature, taking into account that the Gibbs free energy for the diatomic element is 0 kJ/mol:

[tex]\Delta _rG=\Delta _fG_{X}-\frac{1}{2} \Delta _fG_{X_2}=\Delta _fG_{X}[/tex]

Thus, at 2000 K:

[tex]\Delta _rG=\Delta _fG_{X}^{2000K}=4.25kJ/mol[/tex]

And at 3000 K:

[tex]\Delta _rG=\Delta _fG_{X}^{3000K}=-63.12kJ/mol[/tex]

Next, since the relationship between the equilibrium constant and the Gibbs free energy of reaction is:

[tex]K=exp(-\frac{\Delta _rG}{RT} )[/tex]

Thus, at each temperature we obtain:

[tex]K^{2000K}=exp(-\frac{4250J/mol}{8.314\frac{J}{mol\times K}*2000K} )=0.774\\\\K^{3000K}=exp(-\frac{-63120J/mol}{8.314\frac{J}{mol\times K}*3000K} )=12.56[/tex]

In such a way, we can also conclude that at 2000 K reaction is unfavorable (K<1) and at 3000 K reaction is favorable (K>1).

Best regards.

which law states that the pressure and absolue tempeture of a fixed quantity of gas are directly proportional under constant volume conditions?​

Answers

Answer:

Gay lussacs law

Explanation:

Acetonitrile (CH3CN) is an important industrial chemical. Among other things, it is used to make plastic moldings, which have multiple uses, from car parts to Lego bricks. Which one of the following statements about acetonitrile is not correct?a. Acetonitrile has 16 valence electrons in its Lewis structure. b. Acetonitrile has one triple bond. c. Acetonitrile has one pair of nonbonding electrons. d. All atoms satisfy the octet rule in acetonitrile. e. One carbon atom and the nitrogen atom have nonzero formal charges.

Answers

Answer:

One carbon atom and the nitrogen atom have nonzero formal charges.

Explanation:

The compound Acetonitrile has sixteen valence electrons as is easily San from its structure. It contains a carbon nitrogen triple bond with a lone pair of electrons on nitrogen. All atoms satisfy the octet rule and there is no hyper valent atom in the molecule.

The formal charge an carbon and nitrogen is calculated as follows;

No. of valence electron on atom - [non bonded electrons + no. of bonds]

Therefore, for carbon and nitrogen, we have;

formal charge on carbon = 4 - (0 + 4) = 0

formal charge on nitrogen = 5 - (2 + 3) = 0

Hence carbon and nitrogen both possess zero formal charges.

Predict the reactants of this chemical reaction. That is, fill in the left side of the chemical equation. Be sure the equation you submit is balanced.

_______ → Ba(ClO)2 + H2O(l)

Answers

Answer:

2HClO(aq) + Ba(OH)₂(aq) →  Ba(ClO)₂(aq) + 2H₂O(l)

Explanation:

The reaction corresponds to a neutralization reaction between an acid and a base, as follows:

2HClO(aq) + Ba(OH)₂(aq)  →  Ba(ClO)₂(aq) + 2H₂O(l)            

From the equation above we have that the acid HClO reacts with the base Ba(OH)₂ to obtain a salt Ba(ClO)₂ and water.

In the balanced reaction, we have that 2 moles of HClO react with 1 mol of Ba(OH)₂ to produce 1 mol of Ba(ClO)₂ and 2 moles of water.

I hope it helps you!    

A 2.87g sample of carbon reacts with hydrogen to form 3.41g of car fuel. What is the empirical formula of the car fuel?

Answers

Answer:

The empirical formulae for the car fuel is C4H9

In which list are the three compounds above correctly listed in order of increasing boiling point? A) lowest b.p.... isopropanol < isobutane < acetone ...highest b.p. B) lowest b.p.... isobutane < acetone < isopropanol ...highest b.p. C) lowest b.p.... isobutane < isopropanol < acetone ...highest b.p. D) lowest b.p.... acetone < isobutane < isopropanol ...highest b.p. E) lowest b.p.... acetone < isopropanol < isobutane ...highest b.p.

Answers

Answer:

The correct answer is - option B -  lowest b.p.... isobutane < acetone < isopropanol ...highest b.p.

Explanation:

Isobutane has lowest boiling point due to no hydrogen bonding and no diole to dipole interaction found in them. Isobutane only shows weak dispersion force.

Acetone has dipole dipole interaction but due to lack of Hydrogen bonding they have low boiling point than isopropanol but higher than isobutanol.

Isopropanol is the compound that has ability to form hydrogen bonding with other molecule its boiling point is maximum among all three.

Thus, the correct answer is - option B -  lowest b.p.... isobutane < acetone < isopropanol ...highest b.p.

Place the following compounds in order of increasing strength of intermolecular forces. CH4 CH3CH2CH3 CH3CH3 Group of answer choices CH3CH2CH3 < CH4 < CH3CH3 CH4 < CH3CH3 < CH3CH2CH3 CH3CH2CH3 < CH3CH3 < CH4 CH4 < CH3CH2CH3 < CH3CH3 CH3CH3 < CH4 < CH3CH2CH3

Answers

Answer:

CH4 < CH3CH3 < CH3CH2CH3

Explanation:

Alkanes are saturated aliphatic hydrocarbons that undergoes intermolecular Van der waals forces. Van der waals forces are the attractive forces which make it possible for non-polar molecules to form liquids and solids.

Van der waals force are described as intermolecular forces arising from induced fluctuating dipoles in atoms and molecules brought about by movement of electrons around the atomic nucleus.

An example of the Van der waals force is the  london dispersion force that occurs in the alkane family. It is the weakest of all electrical forces that act between atoms and molecules, These forces are responsible for liquefaction or solidification of non-polar substances at low temperature.

The strength of the intermolecular forces is based on the number of electrons surrounding the molecule and the surface area of the molecule. SO, in alkanes, the longer the carbon chain, the more stronger the intermolecular forces.

What element is being reduced in the following redox reaction? MnO4-(aq) + H2C2O4(aq) → Mn2+(aq) + CO2(g) What element is being reduced in the following redox reaction? MnO4-(aq) + H2C2O4(aq) → Mn2+(aq) + CO2(g) H O Mn C

Answers

Answer: Mn is getting reduced.

Explanation:

Oxidation-reduction reaction or redox reaction is defined as the reaction in which oxidation and reduction reactions occur simultaneously.

Oxidation reaction is defined as the reaction in which a substance looses its electrons. The oxidation state of the substance increases.

Reduction reaction is defined as the reaction in which a substance gains electrons. The oxidation state of the substance gets reduced.

[tex]MnO_4^-(aq)+H_2C_2O_4(aq)\rightarrow Mn^{2+}(aq)+CO_2(g)[/tex]

Oxidation : As Manganese has an oxidation state of +7 in [tex]MnO_4^-[/tex] and +2 in [tex]Mn^{2+}[/tex], the oxidation state is decreasing and hence it is getting reduced.

Reduction : As carbon has an oxidation state of +3 in [tex]H_2C_2O_4[/tex] and +4 in [tex]CO_2[/tex], the oxidation state is increasing and hence it is getting oxidized.

The element which is reduced in the redox reaction is Mn.

The redox reaction is shown below:

MnO₄⁻(aq) + H₂C₂O₄(aq) → Mn²⁺(aq) + CO₂(g)

A redox reaction is the type of reaction which involves oxidation processes

occurring with a corresponding reduction process.

Oxidation reaction involves the reaction in which a substance loses its

electrons to become positively charged with an increase in the oxidation

state.

Reduction reaction is defined as the reaction in which a substance gains

electrons to become positively charged with a decrease in the oxidation

state.

MnO₄⁻ has an oxidation state of +7 and Mn²⁺ having an oxidation state of +2

signifies a decrease in the oxidation state.

Read more on https://brainly.com/question/10354645

How do covalent bonds form? A Sharing valence electrons between atoms. B Donating and receiving valence electrons between atoms. C Opposite slight charges attract each other between compounds. D Scientists are still not sure how they form.

Answers

Answer:

A. Sharing valence electrons between atoms.

Explanation:

This is the definition of a covalent bond. Option B describes ionic bonds, Option C describes intermolecular forces, and Option D is wrong because then there wouldn't be any mention of them in our high school chemistry textbooks :).  

How are animals used in vaccine development?

Answers

Answer:

Animals whose certain organs closely match those of humans or have similar genetic makeup are used in vaccine tests because the results can closely resemble those same results on humans.

Explanation:

Answer:

they use them to test the effectiveness of the vaccine.

Explanation:

The type of evaporator that has all saturated liquid entering the evaporator and saturated liquid throughout the evaporator is commonly known as a

Answers

Answer:

Flooded evaporator

Explanation:

It is flooded evaporator because the liquid refrigerant covers the entire heat transfer surface thereby operating with a low pressure receiver.

The receiver acts to separate gaseous and liquid refrigerant after the expansion valve and make sure there is a feed of 100% liquid refrigerant to the evaporator. This make it to have saturated liquid entering the evaporator and saturated liquid throughout the evaporator.

Enter the complementary strand of this DNA strand. Give your answer as a string.

Answers

Answer:

atagcca

Explanation:

t goes with a, and c goes with g

atagcca matches with

ta tcggt

An object has a mass of 4.9g and a volume of 14.ml.what is the density of the object?

Answers

Answer:

0.35 g/mL

Explanation:

Use the formula D = [tex]\frac{m}{v}[/tex], where D is density, m is mass, and v is volume.

D = 4.9/14

D = 0.35

D = 0.35 g/mL

Which of the reactions are spontaneous (favorable)? DHAP↽−−⇀glyceraldehyde-3-phosphateΔG=3.8 kJ/mol C4H4O5⟶C4H2O4+H2OΔG=3.1 kJ/mol C2H4+H2−→−−Rh(I)C2H6ΔG=−150.97 kJ/mol glutamate+NAD++H2O⟶

Answers

Answer:

C₂H₄ + H₂ →−−Rh(I) C₂H₆ Δ

Candle wax melts low temperature, it is not conductive to electricity, it is insoluble in water and partially soluble in solvents nonpolar, like gasoline. Than type of links are present in the candle wax?

A. Electrostatics.
B. Apolar.
C. lónicos.
D. Hydrogen bridges.

Answers

electrostatic and ionic are definitely not the answer because they have high melting point

hydrogen bonds are too weak and not permanent.

so the answer is apolar as it is soluble in polar solvents (water)

Answer:

B. Nonpolar

Explanation:

The low melting point tells you the compound is not ionic, metallic, or a network solid.

It is almost certainly a molecular solid.

It does not conduct electricity, so it is not metallic (which we have already ruled out).

It is insoluble in polar solvents (water) and soluble in nonpolar solvents (gasoline).

Since like dissolves like, the molecule is nonpolar.

The type of links must be nonpolar.

An SN2 reaction is a type of _____________ in which the nucleophile attacks the electrophile.

Answers

Answer:

A bimolecular nucleophilic substitution (SN2) reaction is a type of nucleophilic substitution whereby a lone pair of electrons on a nucleophile attacks an electron deficient electrophilic center and bonds to it, resulting in the expulsion of a leaving group.

Determine the molarity for each of the following solutions A. 1.8×10^4mg of HCL in 0.075L of solutions

Answers

The answer would have to be a

The number of moles of H2O which contains 4g of oxygen?

Answers

Answer:

16G = 1 mole ; then 4G = how many moles? 4/16 = 0.25 mole; That means 4 grams of oxygen is 0.25 moles.

Explanation:

A mole of water molecules contains 2 moles of hydrogen atoms and 1 mole of oxygen atoms.

write the balanced nuclear equation for the radioactive decay of radium-226 to give radon-222, and determine the type of decay

Answers

Answer:

226Ra88→222Rn86+4He2

Explanation:

An α-particle usually consists of a helium nucleus which indicates the type of decay that was undergone in this radioactive process.

During α-decay(alpha decay), an atomic nucleus emits an alpha particle.

Draw the structure of beeswax.beeswax is made from the esterfication of a saturated 16-carbon fatty acid and a 30 carbon straight chain primary alcohol.

Answers

Answer:

Triacontyl palmitate

Explanation:

In this case, we have a reaction between an acid and an alcohol. When we put together these kind of compounds an ester is produced. This reaction is called "esterification".

In our case, the alcohol is a structure with 30 carbon in which the "OH" group is bonded on carbon 1. The name of this compound is "n-triacontanol". The acid is a structure in which we have 16 carbon in which the "COOH" group is placed on carbon 1. The name of this compound is "palmitic acid". The ester produced by the acid and the alcohol is "Triacontyl palmitate".

See figure 1.

I hope it helps!

Which of the following is a salt that could be generated by combining a weak acid and a weak base? Select the correct answer below:
a) NaCl
b) Na2SO4
c) NH4NO3
d) NH4F

Answers

Answer:

d) NH4F

Explanation:

Hello,

In this case, the base resulting from mixing a weak acid and a weak base is d) NH4F since ammonium hydroxide is a wear base and hydrofluoric acid is a weak acid.

Ammonium hydroxide is a weak base since it is not completely ionized in ammonium and hydroxyl ions:

[tex]NH_4OH\rightarrow NH_4^++OH^-[/tex]

Moreover, hydrofluoric acid is a weak acid since it is not completely ionized in hydrogen and fluoride ions:

[tex]HF\rightleftharpoons H^++F^-[/tex]

For the both of the substances, the limit is established by the basic and the acid dissociation constant respectively.

Regards.

A student is performing a Benedict’s test on an unknown substance. He adds the reagent (the chemical required to make a color change), and nothing happens. What can he conclude? A- The substance is glucose-based. B- The substance is not glucose-based. C- The test was inconclusive because he needed to also test with iodine or vinegar. D- The test was inconclusive because he forgot to add heat.

Answers

Answer:

The correct answer is : option D. The test was inconclusive because he forgot to add heat.

Explanation:

Benedict's test is a test that is used to confirm the presence of the simple carbohydrates (mono saccharides and some disaccharides). It is a reagent made by mixture of solution of CuSO4 with sodium citrate and Na2CO3.

Benedict's reagent is added to the substance to test and then heated if it turns yellow to orange or red the presence of simple sugar is confirmed.

Thus, the correct answer is : option D. The test was inconclusive because he forgot to add heat.

Answer:

The test was inconclusive because the student forgot to add heat.

Explanation:

If the test revealed it was not glucose, then the student could run these tests. The student, however, does not need these substances to run the glucose test properly.

The last group of elements on the periodic table are called _____. noble gases halogens metals noble solids

Answers

Answer:

The answer is noble gases

Explanation:

Here is your explanation The vertical columns are called groups. There are eighteen groups. The last group on the far right is called the noble, or inert gases. Elements in a group have similar chemical properties. For example, elements in the noble gas group are all gases under. This is the thing from the passege bye god bless you

The last group of elements on the periodic table are called "noble gases."

The noble gases are a group of elements located in Group 18 of the periodic table. They are also known as Group 0 or the "inert gases." The noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).

The noble gases are unique because they have a full complement of valence electrons in their outermost energy level. This full electron configuration gives them exceptional stability, making them chemically unreactive or inert under normal conditions. In other words, noble gases are less likely to form chemical bonds with other elements.

Learn more about noble gases from the link given below.

https://brainly.com/question/19024000

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A critical reaction in the production of energy to do work or drive chemical reactions in biological systems is the hydrolysis of adenosine triphosphate, ATP, to adenosine diphosphate, ADP, as described by the reaction

ATP(aq)+H2O(l)→ADP(aq)+HPO2−4(aq) for which ΔGrxn=30.5 kJ/mol at 37.0∘C and pH 7.0.

Required:
Calculate the value of ΔGrxn in a biological cell in which [ATP]=5.0 mM, [ADP]=0.60 mM, and [HPO2−4]=5.0 mM

Answers

Answer:

ΔG  = -49.64 KJ/mol

Explanation:

The actual free energy change of the reaction under the given conditions,  ΔG is given by the formula below;

ΔG = ΔG'° + RT ln([ADP][HPO₂⁴⁻] / [ATP])

where ΔG'° = -30.5 KJ/mol; R = 8.315 J/mol.K; T = 37°C = 310 K; [ADP] = 5.0 mM = 0.005 M; [HPO₂⁴⁻] = 0.60 mM = 0.0006 M; [ATP] = 5.0 mM = 0.005 M

ΔG = -30.5 KJ/mol + (8.315 J/mol.K)(310 K) ln {(0.005)(0.0006)/(0.005)}

ΔG = -30.5 KJ/mol + (2.58 KJ/mol * -7.4186)

ΔG = -30.5 KJ/mol - 19.14 KJ/mol

ΔG  = -49.64 KJ/mol

The insoluble salts below are put into 0.10 M hydrochloric acid solution. Do you expect their solubility to be more, less, or about the same as in a pure water solution?
1. Zinc sulfide
2. Silver chloride
3. Lead iodide
4. Silver hydroxide

Answers

Answer:

1. Zinc sulfide : about the same solubility, no common ion is found.

2. Silver chloride : less solubility due to the presence of chloride ions provided by the 0.10 M hydrochloric acid.

3. Lead iodide  : about the same solubility, no common ion is found.

4. Silver hydroxide : about the same solubility, no common ion is found.

Explanation:

Hello,

In this case, we first must remember that adding a common ion (which is related with the dissolving solid) decreases the solubility of the insoluble solid due to the fact Le Chatelier's principle states the reaction will shift leftwards (reactants) to reestablish equilibrium, therefore, we have:

1. Zinc sulfide : about the same solubility, no common ion is found.

2. Silver chloride : less solubility due to the presence of chloride ions provided by the 0.10 M hydrochloric acid.

3. Lead iodide  : about the same solubility, no common ion is found.

4. Silver hydroxide : about the same solubility, no common ion is found.

Best regards.

A student puts a glass of water in the freezer. Later, he notices ice forming on the surface of the water. Which property of water best explains why ice forms on its surface? A. It is made of polar molecules. B. It has low surface tension. C. It has weak adhesion. D. It is densest as a solid.

Answers

ℯ ℴ ℴ ℴℯℯ

it has a weak adhesion

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Consider the following ordered data. 6 9 9 10 11 11 12 13 14 (a) Find the low, Q1, median, Q3, and high. low Q1 median Q3 high (b) Find the interquartile range. John and Fred owned, as joint tenants with right of survivorship, business property that they purchased for $40,000. John furnished one fourth of the purchase price and Fred furnished three fourths of the purchase price. Depreciation deductions allowed before Fred's death were $8,000. Under local law, each had a one half interest in the income from the property. At the time of Fred's death, the fair market value of the property was $80,000, three fourths of which is includable in Fred's estate. What is John's basis in the property at the date of Fred's death A report states that the mean yearly salary offer for students graduating with a degree in accounting is $48,722. Suppose that a random sample of 50 accounting graduates at a large university who received job offers resulted in a mean offer of $49,870 and a standard deviation of $3900. Do the sample data provide strong support for the claim that the mean salary offer for accounting graduates of this university is higher than the national average of $48,722? Test the relevant hypotheses using = 0.05. State your conclusion.A. Reject H0. We do not have convincing evidence that the mean salary offer for accounting graduates of this university is higher than the national average of $48,722.B. Do not reject H0. We do not have convincing evidence that the mean salary offer for accounting graduates of this university is higher than the national average of $48,722.C. Reject H0. We have convincing evidence that the mean salary offer for accounting graduates of this university is higher than the national average of $48,722.D. Do not reject H0. We have convincing evidence that the mean salary offer for accounting graduates of this university is higher than the national average of $48,722. what mode of nutrition is house fly Characteristics caused by hormones but that do not include development of reproductive organs are called A. primary sex characteristics. B. secondary sex characteristics. C. physical characteristics. D. body characteristics. What is the primary focus of the image? What colors are emphasized in the image, and how do they contribute to the subject? What details are absent from the image? What do the details in the image convey about the subject? What is the overall mood of the image? And about the picture just search up "Earthrise." I need someone to answer this question for me correctly please? What shape best describes the cross-section cut at an angle to the base of a right rectangular prism? Trapezoid Parallelogram Square Rectangle An atom of 108Te has a mass of 107.929550 amu. Calculate the binding energy per MOLE in kJ. Use the values: mass of 1H atom whats suface tension Which of the following perspectives from the balanced scorecard approach helps managers answer the question, "How do we look to shareholders?a. Learning and growth perspective b. Internal business perspective c. Customer perspective d. Financial perspective ON TEST HELP!Which option in the Caption dialog box configures whether the caption appears above or below the image?O LabelO New LabelO PositionO Numbering -36 4/9 - (-10 2/9)-(18 2/9) the sum of three consecutive numbers is 276. What is the smallest of these intengers? Rainsfords response to Zaroff indicates that he is opposed to the idea of hunting humans. he does not understand that Zaroff is hunting humans. he will soon be joining Zaroff in the hunt for humans. he thinks Zaroff has the right to hunt humans PLEASE HELP TO BE MARKED THE BRAINLIEST Advertising could be referred to as _____________________. making the existence of a commodity known to the public and encouraging them to buy getting the government informed about the procedures in courts none of the options making the closure of manufacturing concern Subtract 5p + 8q from the sum of 5p + 4q and 9p + 69. Your car must have two red stoplights, seen from ______ feet in the daytime, that must come on when the foot brake is pressed.A. 100B. 200C. 300D. 400 Subjects and verbs must agree in which of the following categories? 1 singular 2 phrase 3 number 4 plural