Answer
$\Delta U_{neon}=197.73\ kJ$
The change in internal energy would be different because the heat capacity would be different.
Work Step by Step
Assuming in both cases $c_{v,avg} \approx c_{v,300K}$
$\Delta U=mc_v\Delta T$
With $m = 2kg, \Delta T=160\ K $
For neon ($c_v = 0.6179\ kJ/kg.K$):
$\Delta U=197.73\ kJ$
For argon ($c_v = 0.3122\ kJ/kg.K$):
$\Delta U=99.90\ kJ$
