How would you know if this combination is likely to be found in some dirt?

  very unlikely to be found in dirt

Explanation:

That combination has a ratio of ¹⁴N to ¹⁵N of 10:4 = 2.5: 1. The most ¹⁵N enriched natural material has a ratio of ¹⁴N to ¹⁵N on the order of 250 : 1 or higher. The combination shown is very unlikely to be found in dirt.

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.