Nitrogen and hydrogen combine to produce ammonia. n2 + h2? nh3which set of coefficients balances the equation?

The equation for the production of Ammonia is:
     N₂  +  H₂  →  NH₃

N₂  +  H₂   (LeftHandSide of equation) : 2 Nitrogen atoms; 2 Hydrogen atoms
NH₃ (RightHandSide of equation): 1 Nitrogen Atom; 3 Hydrogen atoms
   
To balance the equation you must place in front of each compound/molecule/element that makes the amount of atom of each element equal on both sides of the equation.

N₂  +  3H₂  →  2NH₃

                          LHS         RHS
Nitrogen              2             2
Hydrogen            6             6

So essentially the set of coefficients you use to balance the equation are 1 for N₂, 3 for H₂ and 2 for NH₃.