What is the number at the end of an isotope’s name?

Explanation:

5 I don't know what is the answer if I got it wrong

The number of protons and electrons remain same for two isotopes. This means isotopes have different mass number but have same atomic number. When we write an isotope, the number at the end of the isotope's name is the mass number.

the reaction mixture contains some ammonia, plus a lot of unreacted nitrogen and hydrogen. the mixture is cooled and compressed, causing the ammonia gas to condense into a liquid. the liquefied ammonia is separated and removed. the unreacted nitrogen and hydrogen are then recycled back into the reactor .