Which is the most important question for deciding if a chemical reaction has occurred? was there a change in the size? was any heat energy given off? what is the density of the substance? what is the texture of the substance?

Option (b) is the correct answer.

Explanation:

A chemical reaction can be exothermic or endothermic in nature. That is, if there is release of energy during a chemical reaction then the reaction is exothermic.

If there is absorption of energy during a chemical reaction then the reaction is endothermic in nature.

Thus, when we ask was any heat energy given off? Then, we are talking about a chemical reaction which has occurred.

Option (b) is the correct answer.

Explanation:

what is the volume occupied by 40 grams of argon gas (ar) at standard conditions? what volume, in liters, is occupied by 1.5 x 1023 

i think it's letter a.