The chemical equation represents the reaction describes is;
4NH3 + 5O2 = 4NO + 6H2O
Therefore 4 moles of NH3 reacts with 5 moles of O2.
1 mole of O2 (molar mass) = 2 * 16 = 32g.
5 moles of O2 = 5 * 32 = 160g
4 moles of NH3 = 4 (14 + 3*1) = 68g
Therefore, 68g of NH3 reacts with 160g of O2.
But, we have only 4.5 g of oxygen.
68g reacts with 160g
Xg reacts with 4.5
X = 68*4.5 / 160 = 1.9125g
        
             
        
        
        
All group 7 elements are members of the halogen family, seen on the periodic table of elements. Such as : F, Cl, Br.
        
             
        
        
        
Answer:
General chemical equation 
           2 M + 3 X₂ → 2 MX₃
Explanation:
When metal reacts with halogens metal halide as a product obtained.
Now oxidation state of metal assume (+3)
and oxidation state  for halogen = (+1)
So formula of the metal halide is (MX₃)
            Denote the metal as M and halogen as X
                     the balanced chemical equation
                          2 M + 3 X₂ → 2 MX₃
So the resulted general equation when metal react with halogen is 
                                        2 M + 3 X₂ → 2 MX₃