Answer
See the answer below.
Work Step by Step
Number of moles of air:
$n=PV/RT$
$n=1.0\ atm×1\ km^3×1×10^{12}\ L/km^3/0.082057\ L.atm/mol.K/(25+273)\ K$
$n=4.09×10^{10}\ mol$
Number of moles of methane:
$4.09×10^{10}\ mol_{air}×177.4\ mol_{CH_4}/10^9\ mol_{air}=7255\ mol$
A) Number of molecules:
$7255\ mol×6.022×10^{23}\ molecules/mol=4.44×10^{27}\ molecules$
B) From stoichiometry, the number of moles of methane and methylphosphonate are the same:
$7255\ mol×95.01\ g/mol=689.3\ kg$
