Answer is: the molecular mass ratio of two gases is 1 : 256.
rate of effusion of
gas1 : rate of effusion of gas = 16 : 1.
rate of effusion of gas1 = 1/√M(gas1).
rate of effusion of gas2 = 1/√M(gas2).
rate of effusion of gas1 = rate of
effusion of gas2 · 16.
1/√M(gas1) = 1/√M(gas2) · 16 /².
1/M(gas1) = 1/M(gas2) · 256.
M(gas1) · 256 = M(gas2).
