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.