Explanation

(c) Mean kinetic energy of gas molecule
$E = \frac{f}{2}kT = \frac{f}{2}k(t + 273) = \left( \frac{f}{2}k \right)t + \frac{f}{2} \times 273k;$
Comparing it with standard equation of straight line
$y = mx + c.$ We get $m = \frac{f}{2}k$ and $c = \frac{f}{2}273k$
So the graph between $E$ and $t$ will be straight line with positive intercept on $E$-axis and positive slope with $t$-axis