Please note that, I apply the equation of gases, as below:
P*V=n*R*T, where n is the number of mol of the gas, V is the volume occupied by the gas, P is the pressure exerted by the gas, R is the constant of the gases, namely R = 0.08206 liter*atm/ °K. So we have:
n = (P*V)/(R*T) = (0.68 * 8.1562) /( 0.08206*372.85) = 0.18 mol of H2 gas
then the mass of H2 is 0.18* 2 = 0.36 grams
Please note thatthe pressure is 69490/101325 = 0.68 atm
and the temperature is:
273.15+99.7= 372.85 °K
here we have molecular mass of ammonia (NH3) = 17,
so n= (P*V) / (R*T)= (1*2.04)/(0.08206*273.15) = 0.091 mol of NH3,
so the mass of ammonia is 0.091 * 17 = 1.55 grams of NH3 gas.
Please note that the STP condition are T = 273.15 °K and P = 1 atm.