A 500 mL glass flask is filled at 298 K and 1 atm, pressure with three diatomic gases, X, Y and Z . The initial volume ratio of the gases before mixing was 5:3:1 .The density of the heaviest gas in the mixture is not more than 25 times that of the lighest gas. When the mixture was heated, vigorous reactions take place between X and Y and X and Z in which all the three gases were completely used up. The gases X,Y, Z respectively are
A. `H_2, O_2 , N_2`
B. `H_2 , O_2 , Cl_2`
C. `H_2 , F_2 , O_2`
D. `O_2,H_2 , F_2`
