7g of nitrogen occupies a volume of 5 litres under certain conditions.  Under the same conditions one mole of a gas, having molecular weight 56, occupies a volume of

7 gms of $N_2$ occupies 5 lit

 $\therefore$ 28 gms (mol. wt) of $N_2$ occupies 20 lit

  $\therefore$ According to Avogadro’s law equal no. of moles occupies equal volume.

 $\therefore$  gas also occupies 20 lit.