a
$P \propto T$
$\Rightarrow$ $\frac{{{P_1}}}{{{P_2}}} = \frac{{{T_1}}}{{{T_2}}}$
$\Rightarrow$ $\frac{{{P_2} - {P_1}}}{{{P_1}}} = \frac{{{T_2} - {T_1}}}{{{T_2}}}$
$\Rightarrow$ $\left( {\frac{{\Delta P}}{P}} \right)\,\% $$ = \left( {\frac{{251 - 250}}{{250}}} \right) \times 100$ $= 0.4 \%$