Answer
See the answer below.
Work Step by Step
a) rms speed is inversely proportional to the molecular weight:
$CO_2\lt O_2\lt C_2H_6\lt H_2O$
b) Number of moles of ethane:
$n=(256/760×1\ atm)×3.26\ L\div 0.082057\ L.atm/mol.K\div 298\ K$
$n=0.045\ mol$
Stoichiometric proportions:
$0.045\ mol×9/2=0.158\ mol\ O_2$
Total number of moles: $0.202\ mol$
Final pressure:
$P=0.202\ mol×0.082057×298\ K/3.26\ L$
$P=1.51\ atm=1152\ mmHg$
Partial pressure of oxygen:
$1152\ mmHg×7/9=896\ mmHg$
