If the heat of reaction is negative, the reaction is select one: a. positive b. exothermic c. endothermic d. negative

Option (b) is the correct answer.

Explanation:

A chemical reaction where heat energy is absorbed by the reactant molecules is known as an endothermic reaction.  

For example,

The value of = +ve for an endothermic reaction.

In an endothermic reaction, heat being absorbed is utilized to break the bonds. Therefore, temperature of the system decreases.  

On the other hand, a chemical reaction in which heat energy is released by the reactant molecules is known as an exothermic reaction.  

The value of = -ve for an exothermic reaction.

Thus, we can conclude that if the heat of reaction is negative, the reaction is exothermic.

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

tracks, burrows, eggshells, nests, tooth marks, or gastroliths