What volume would a 0.250 mole sample of h2 gas occupy, if it had a which has a pressure of 1.70 atm, and a temperature of 35 °c?

The volume that  would  be  occupied   by  0.25  moles   sample  of  H2  is    calculated  using  ideal  gas  equation  formula

that is  PV  =nRT

P(pressure)=  1.7  atm
V( volume)? 
n(number of moles)= 0.250  moles
R(gas  constant)=0.0821  l.atm/mol.K
T (temperature in  kelvin)=35+273  =  308k

by  making V the  subject  of the  formula V=nRT/P

=(0.250  moles  x  0.0821  L.atm/k.mol  x 308 k)/( 1.70 atm)  = 3.7  L  of  H2  gas

They carry out the exchange of gases as we breathe ( oxygen and carbon dioxide).