15. D is correct, exothermic reactions release heat
I am not sure about 16
The is the B) doing background research about the question
Answer: 2.88×
atoms 
Explanation: First, using stoichiometry, we must convert this from grams to moles, then from moles to atoms.
1. For the first step, we should also look at the periodic table to find the molar mass of the compound, then use that as the denominator.

2. Now that it is converted to moles, we must convert it to atoms by multiplying it by Avogadro's number.

With this information, we know that there are
total atoms in 0.680 grams
.
I hope this helps! Pls give brainliest!! :)
The following quantities will effect the reaction rate as follows:
1. On increasing Concentration of the reactant: Rate of the reaction will increases.
2. On increasing pressure : Increases the rate of reaction to the side where there are fewer number of molecules.
3.On increasing temperature of an endothermic reaction: Increases the rate of reaction
4. On decreasing temperature of an endothermic reaction: Increases the rate of reaction.
So the answer is increase pressure, decrease temperature, increase concentration will increases the rate of the reaction.