b
$PV = \mu \,RT = \frac{m}{M}RT$
$\Rightarrow$ $\frac{m}{{VP}}$ $\Rightarrow$ $\frac{{density}}{{P}} = \frac{M}{{RT}}$
${\left( {\frac{{density}}{P}} \right)_{at\,0^\circ C\;}} = \frac{M}{{R(273)}} = x$ …...$(i)$
${\left( {\frac{{density}}{P}} \right)_{at\,100^\circ C\;}} = \frac{M}{{R(373)}}$ …..$(ii)$
$\Rightarrow$ ${\left( {\frac{{density}}{P}} \right)_{at\,100^\circ C\;}}$$ = \frac{{273x}}{{373}}$