How many gm of 83.4% pure sodium sulphate can be produced from 250 gms of 95% pure NaCl

 $2NaCl+H_{2}S{O}_4\to N{a}_{2}S{O}_4+2HCl$
Amount of Pure  $NaCl=250\times \frac{95}{100}=237.5gms$
$2\times 58.5gmNaCl\to 142gmN{a}_{2}S{O}_4$
$237.5gmNaCl\to 288.2gmN{a}_{2}S{O}_4$
To get 83.4 gm pure  $N{a}_{2}S{O}_4$ take 100 gms of impure sample to get 288.2 gms pure $N{a}_{2}S{O}_4$ take 345.4 gm of impure sample