c
$PV = \frac{m}{M}RT$ $\Rightarrow$ $V \propto mT$
$\Rightarrow$ $\frac{{{V_1}}}{{{V_2}}} = \frac{{{m_1}}}{{{m_2}}}.\frac{{{T_1}}}{{{T_2}}}$
$\Rightarrow$ $\frac{{2V}}{V} = \frac{m}{{{m_2}}} \times \frac{{100}}{{200}}$
$\Rightarrow$ ${m_2} = \frac{m}{4}$