In the reaction below, how would adding more of product C affect the equilibrium of the system? (2 points)
A + B ⇄ C + D
Select one:
a. Shift it to the right toward the products.
b. Shift it to the left toward the reactants.
c. Equally create more products and reactants.
d. It would have no effect.

In the endothermic reaction below, how would adding heat affect the equilibrium of the system? (2 points)
A + B + energy ⇄ + D
Select one:
a. Shift it to the left toward the reactants.
b. Shift it to the right toward the products.
c. Equally create more products and reactants.
d. It would have no effect.

In the following reaction, if you wanted to produce more hydrochloric acid (HCl), what should you do? (2 points)
4HCl + O2 ⇄ 2H2O + Cl2
Select one:
a. Add more H2O
b. Add more O2
c. Remove H2O
d. Remove Cl2

All the given reactions are reversible in nature.
In a reversible chemical reaction, the shift of equilibrium of the reaction towards the production of products or reactants is dependent on the abundance of reactants or products.
As in the first question, if the products available are more (C) than the reactants, then the equilibrium of the reaction would shift towards the formation of the reactants (A and B).
As in second question, if reactants available are more (heat addition) than that of products, then the equilibrium of the reaction would shift towards the formation of products (D).
As in the third question, we want to generate more HCL, which is the reactant, so we need to increase the amount of product, so we need to add more H2O.