Activation energy:.a) is the energy needed by an enzyme to catalyze a reaction without coenzymes. b) given off as the products in a chemical reaction are formed. c) required for a chemical reaction to begin. d) absorbed as ΔG0 moves from negative to positive.

c) required for a chemical reaction to begin.

Explanation:

Activation energy is the minimum amount of energy required to initiate a chemical/bio-chemical reaction. Most of the reactions are slow because they require a lot of energy to get initiated. So in order to initiate reaction, enzymes provide an alternate pathway which requires comparatively less amount of energy. Substrate of a reaction binds to the enzyme which results in change of shape of the substrate in such a manner that ultimately causes activation energy to get lowered. In short we can say that enzyme holds the substrate in such a manner that requires less activation energy and hence increases the catalysis.

b. read the phase at the intersection of any given temperature and pressure.