At STP 22400 mL is occupied by 1 mole of a gas
Therefore, number of moles of hydrogen gas in 225 ml ( 225 cm3) = (1/22400) 225
= 0.01
Now,
760 mm Hg = 1 atm
810 mm Hg = 1.065 atm
97 degree Celsius = 273 + 97 = 370 K
Applying,
PV = nRT
V = (0.01 0.0821 370) / 1.065
= 0.2852 L
= 285.2 mL