The answer for #3 is c but i don't know why

I’m an electrically neutral atomic any element, there are equal numbers of

4.25g sample of solid ammonium nitrate dissolves in 60.0g of water in a coffee-cup calorimeter, the temperature drops from 22.0 c to 16.9 c. assume that the specific heat of the solution is the same as that of pure water. calculate delta(h) (in kj/mol nh4no3) for the solution proces.

Which radioisotope is used to date fossils? a. oxygen-16 b. carbon-14 c. uranium-238 d. carbon-12