_N₂+_H₂→ _NH₃
Balance equation

Hi not sure if this helps bu This reaction is the synthesis of Ammonia using Nitrogen and Hydrogen gas.
N+H→NH3
We must remember that Nitrogen and Hydrogen are both diatomic molecules in their standard gas form. This adjusts the equation to
N2+H2→NH3
Now we need to adjust coefficients in order to balance the atoms on each side of the equation. Currently we have 2 atoms of nitrogen and 2 atoms of hydrogen on the reactant side and 1 atom of nitrogen and 3 atoms of hydrogen on the product side.
We can balance the hydrogens by placing a coefficient of 2 in front of ammonia and a coefficient of 3 in front of the hydrogen.
N2+3H2→2NH3
This gives us 6 hydrogen on each side and coincidentally the nitrogens now equal 2 on each side.

Ithink the answer is d