Answer
Density of $N_{2}$= 1.38 g/L
Density of air= 1.44 g/L
Work Step by Step
Recall: $d=\frac{PM}{RT}$ where $d$ is the density, $P$ is the pressure, $M$ is the molecular weight, $R$ is the universal gas constant and $T$ the temperature in K.
Given/Known: $P=1.25\,atm$
$R=0.0821\,L\,atm\,mol^{-1}K^{-1}$ and
$T=(35+273)K= 308\,K$
For $N_{2}$, $M= 28.0\,g/mol$ and
$d=\frac{1.25\,atm\times28.0\,g/mol}{(0.0821\,L\,atm\,mol^{-1}K^{-1})(308\,K)}$
$=1.38\,g/L$
For air, $M= 29.2\,g/mol$ and
$d=\frac{1.25\,atm\times29.2\,g/mol}{(0.0821\,L\,atm\,mol^{-1}K^{-1})(308\,K)}$
$=1.44\,g/L$
