Is n2 + 3h2 →2nh3 a balanced chemical equation? is it obeying the law of conservation of matter?

Yes, this is a balanced chemical equation, and it obeys the Law of Conservation of Mass.

A balanced chemical equation obeys the Law of Conservation of Mass if there are the same numbers of each type of atom on each side of the reaction arrow.

N₂ + 3H₂ ⟶ 2NH₃

Let’s check the numbers.

Atom  On the left  On the right

   N            2                 2

   H            6                 6

We have the same numbers of H and O on each side of the reaction arrow.

The equation is balanced and it obeys the Law of Conservation

of Mass.

i believe the answer is true.