Nh3 + o2  → no + h2o the equation is unbalanced. which of the following is the correct balanced equation?

You did not post up the options, however we can balance this equation ourselves simply by adding multipliers to the front of each reactant and product until all atoms balance. Start with one atom type, say hydrogen, then move to the next and next and keep repeating this process.

2NH3 + O2 ⇒ 2NO + 3H2O

This balances nitrogens and hydrogens, but we still can't balance oxygen, so have to multiply up further

4NH3 + 5O2 ⇒ 4NO + 6H2O

This now balances all 3 atom types for reactants and products.

Where’s the selection?