પાણીના મોલ $=\frac{1000}{18}$
ઇથેનોલના મોલ-અંશ $=\frac{\frac{W}{46}}{\frac{W}{46}+\frac{1000}{18}}$
$\therefore 0.2=\frac{1}{5}=\frac{\frac{W}{46}}{\frac{18 W+46000}{46 \times 18}}$
$\therefore 18\,W +46000=90\,W$
$\therefore W=\frac{46000}{72}=\frac{5750}{9}$
$=638.89\,g$
[અણુ દળ - ${Na}: 23.0\, {u}, {O}: 16.0\, {u}, {P}: 31.0 \,{u}]$
$^{200}X \,:\, 90\%$ $^{199}X\, :\, 8.0\%$ $^{202}X\, :\, 2.0\%$