The moles of hydrogen that contained in 1.55 L calculated using the ideal gas equation
that is PV =nRT where n is number of moles
by making n the subject of formula n = Pv/RT
P= total pressure - partial pressure of water vapor = 755-24 = 731 torr
V=1.55 l
T=298 k
R (gas Constant)= 62.364 l.torr/mol.k
n= (731 torr x 1.55 L)/( 62.364 l.torr/mol.k x298 K ) = 0.06 moles of hydrogen