Answer
Helium.
Work Step by Step
$\Delta s = c_p\ln\left(\dfrac{T_2}{T_1}\right)-R\ln\left(\dfrac{P_2}{P_1}\right)$
For He: $c_p=5.1926\ kJ/kg.K,\ R=2.0769\ kJ/kg.K$
For $N_2$: $c_p=1.056\ kJ/kg.K,\ R=0.2968\ kJ/kg.K$
Given $T_1=27°C,\ T_2=427\ °C,\ P_1=200\ kPa,\ P_2=2000\ kPa$:
$\Delta s_{He}=0.3826\ kJ/kg.K$
$\Delta s_{N_2}=-0.2113\ kJ/kg.K$
$\Delta s_{He}\gt\Delta s_{N_2}$
