The correct option is D 16
We know, value of ml varies from −l to +l.
For ml= +1, minimum value of l= 1.
l= 1 corresponds to p-orbital and each p-subshell has 2 electrons with ml value +1.
So, we need two p-subshells in order to have 4 electrons with ml=+1.
1s22s22p63s23p4 have 4 electrons having ml=+1.
Therefore minimum atomic number of element having ml=+1 is 16.