In living cells, atp stores the energy that a. spontaneous reactions release b. spontaneous reactions absorb c. cells radiate as heat d. cells absorb from sunlight

ATP is short for adenosine triphosphate
Adenosine triphosphate converts to either the adenosine diphosphate (ADP) or adenosine monophosphate (AMP), in this process energy is released (for example  glycolysis, the citric acid cycle or oxidative phosphorylation and beta-oxidation). 

ATP is made of three components: the triphosphate, the sugar ribose and a nitrogenous base (adenine).

208 g/mol and 87 g/mol

Explanation:

Number of protons = 82

Atomic mass = 126 + 82 = 208 g/mol

For ^{87}Sr

Number of neutrons = 49

Number of protons = 38

Atomic Mass = 49 + 38 = 87 g/mol