Answer
The temperature will decrease.
Work Step by Step
The enthalpy of steam at $2\ \mathrm{MPa}$ and $T=500^{\circ} \mathrm{C}$ is $h=3468.3\ \mathrm{~kJ} / \mathrm{kg}$. Now consider a throttling process from this state to $1.8\ \mathrm{MPa}$, which is the next lowest pressure listed in the tables. The temperature of the steam at the end of this throttling process will be $$
\left.\begin{array}{l}
P=1.8\ \mathrm{MPa} \\
h=3468.3\ \mathrm{~kJ} / \mathrm{kg}
\end{array}\right\} T_2=499.0^{\circ} \mathrm{C}
$$ Therefore, the temperature will decrease.
