Reactant concentration, along with activation energy and temperature, is a major determinant in reaction rate, as demonstrated in Le Chatlier's principle.

This question can be approached two different ways. One way is by looking at the equation, and the other is understanding what the variables in the equation represent.  

1) The first method is understanding the equation. Because we must understand basic log and natural log functions, we know that the natural log of a fraction is a negative number. Additionally, because we know that a reaction is spontaneous when  is negative, we can conclude that a reaction will be spontaneous when Q is less than K_eq. R is a positive constant, and T cannot be negative.

2) A second approach to this question is understanding the variables in the equation. K_eq is the ratio of product to reactant at equilibrium. Q is the reaction quotient, and represents the ratio of product to reactant at a given point in time. If Q is less than K_eq, the reaction is still too far to the left, and is still reacting to reach equilibrium. Because the reaction is trying to reach equilibrium, it will continue to spontaneously react until it reaches that point. 

The reaction with the fastest rate will have the lowest activation energy; the energy difference between the starting compound and the top of the energy barrier that must be overcome to proceed to the product should be the smallest. Of the given choices, the reaction proceeding from C to D has the lowest energy barrier, and hence will have the lowest activation energy and fastest reaction rate.

In contrast, the energy required to move from point A to point B has the largest energy barrier, and can be assumed to be the rate-limiting step.

If you thought all of these factors are used in the Arrhenius equation, consider that the rate constant is independent of the reactant concentrations. The concentration effect is considered in the rate law by multiplying the concentrations by the constant, but the concentrations themselves are independent of the actual Arrhenius calculation.

The calculation shows that . In this equation, is the activation energy and is the temperature.

The amount of energy released or absorbed by a reaction is independent of its rate. Rate is principally determined by the activation energy, while the inherent bond energies of reactants and products dictate thermodynamic changes. One cannot be used to predict the other.

Reaction rates, including the rate-determining step, can be altered with a change in conditions. This includes a change in temperature, a change in pressure, or the addition of a catalyst.

For a multi-step reaction, the rate-determining step is the step with the highest activation energy. Be careful not to confuse this with the energy transition state.

A catalyst is used to increase the rate of a reaction. By definition, it does so without being consumed during the reaction. Thus the choices that talk about decreasing the rate of reaction are wrong. Catalysts decrease the activation energy of a reaction.

The concentration of the enzyme is independent of the rate constant because the enzyme can only catalyze the conversion of reactants to products at a specific rate. Increasing the concentration of the enzyme, however, would increase the absolute number of reactions occurring simultaneously; thus, the rate of reaction (but not the rate constant) would increase.

This question asks us how the rate of the reaction would change if temperature were increased. Increasing the temperature increases the relative velocity of each reactant, increasing the chance that two reactants collide and are able to form a product with the help of carbonic anhydrase. This can also be seen with the following equation.

Increasing the temperature decreases the denominator because e^E/RT becomes e⁰ = 1 as the temperature increases. The overall effect is an increasing in reaction rate.

Note however, that the temperature can only increase up to a point. Once the temperature becomes too high, the enzyme would denature and no longer work.