What is a redox reaction? A. A reaction in which an element in one molecule is traded for an element in another.
B. A reaction in which the number of protons changes between the reactant and product
C. A reaction in which the oxidation state of one element increases and another decreases
D. A reaction in which an element changes phases when going from reactant to product.

A reaction in which the oxidation state of one element increases and another decreases

Explanation:

Redox reaction means both oxidation and reduction take place in that reaction.

So when an element oxides its oxidation state increases and when an element reduces its oxidation state decrease.

d.) the average kinetic energy of the gas particles is greater in container b because its particles move faster.