Answer
Gas temperature is $270K$
Work Step by Step
From the graph, $v_{p}=400m/s$
Molecular mass of $N_{2}=M= 28g/mol=0.028kg/mol$
Now, we know $v_{p}=\sqrt (2RT/M)$
or, $T=\frac{1}{2}\frac{Mv_{p}^{2}}{R}= \frac{1}{2\times8.314}\times28\times400\times400= 270K$
