$C : H : N : O =\frac{20}{12}: \frac{6.67}{1}: \frac{46.67}{14}: \frac{26.66}{16}=1: 4: 2: 1$

Empirical formula $= CH _4 N _2 O$. So, empirical weight $=60 \,g$.

Given, molecular weight $=60\, g$.

Molecular formula $=(\text { Empirical formula })_{ n }$

$n =\frac{\text { Molecular weight }}{\text { Empirical weight }}=\frac{60}{60}=1$

So, molecular formula is $\left( NH _2\right)_2 CO$.