Consider the reaction ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\to 2{\mathrm{NH}}_3\left(\mathrm{g}\right)$

$n_{0}1.5\mathrm{mol}1.5\mathrm{mol}$

with the progress of reaction it is found that there is a formation of 0.8 mol of ${\mathrm{NH}}_3$ At this stage, the extent of reaction is