Is 2h2 + o2 2h2o 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.

2H₂ + O₂ ⟶ 2H₂O

Let's check the numbers.

Atom On the left On the right

H 4 4

O 2 2

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

The equation is balanced and it obeys the Law of Conservation of Mass.