Equal amounts of four different substances (A-D) where added separately to equal amounts of an acid and a thermometer placed in the mixture. For which substance is the reaction the most endothermic?

A. temperature rises by 5oC
B. temperature falls by 3oC
C. temperature rises by 3oC
D. temperature falls by 5oC

D

Explanation:

An endothermic reaction is one in which there is a temperature fall and the reaction vessel becomes colder. For example, adding potassium iodide crystal to water in a beaker, the beaker becomes cold.

Now, to the question: The most endothermic reaction is the one with the largest temperature drop

A is wrong, temperature rises , it is exothermic

B is endothermic but not correct

C is wrong, temperature rises, it is exothermic

D is correct, temperature falls, It is endothermic and has the largest temperature drop, so we pick it

it is stable as it is in group 0 which have full outer shells of electrons