Both gas A and Hydrogen (H₂) gas have same volume at same pressure. Let both 's volume is V and pressure P.

For gas A :

Pressure = P

Temperature (T) = 300 K

Volume = V

Mass = 3 g

Molar mass = M gm/mol

using ideal gas equation,

PV = nRT

..... (1)

For Hydrogen,

Pressure = P

Temperature (T) = 200 K

Volume = V

Mass = 0.2 g

Molar mass = 2 gm/mol

Using ideal gas equation,

...... (2)

From (1) and (2), we get

M = 45