Assign the position of the element having outer electronic configuration ${\mathrm{ns}}^2{\mathrm{np}}^4\text{ for }\mathrm{n}=3$

The configuration ${\mathrm{ns}}^2{\mathrm{np}}^4$ for n = 3 means element belongs to third period. Since, last electron enters in the p-orbital, it belongs to p-block. For p-block elements, the group number = 10 + valence shell electrons 

=10+(2+4)=16
Hence, the element belongs to 16th group.