(a) In ammonia (NH3) , N and H present in fixed ratio which supports the law of definite or constant proportions.
This law states, “a pure chemical compound always consists of the same elements that are combined together in a fixed proportion by mass”.
(b) Molecular mass of ammonia (NH3)
= mass of N + mass of H
= 14 + ( 3 × 1)
To react with 14 g N, mass of H required = 3 g
Therefore to react with 42 g N, mass of H required
= 3/ 14 ×42