Which answer below correctly gives the chemical reaction for the enthalpy of formation of NH3(g)? N (9) +H2(9) - NHz(9) NG(g) + 3 H (g) - 2 NH (g) 2 NH2(9) - N2(9)+ 3 H2(9) 1/2N2,(g) + 3/2 H2(0) - NH;(9)