The kinetic energy of  'N' molecules of ${\mathrm{H}}_2$ is 3J at -73°C. The kinetic energy of the same sample of  ${\mathrm{H}}_2$ at 127°C is

Kinetic energy=$\frac{3}{2}\mathrm{nRT}$

Kinetic energy is directly proportional to temperature

$\frac{{\mathrm{KE}}_1}{{\mathrm{kE}}_2}=\frac{{\mathrm{T}}_1}{{\mathrm{T}}_2}$

$\frac{3}{{\mathrm{KE}}_2}=\frac{200}{400}$

${\mathrm{KE}}_2$=6 J

Hence the required option is B