A metal has electronic configuration ${\left[Ar\right]}^{18}3d^{7}4s^2$ .  On the basis of this electronic configuration find out the group number

Last electron enters in d-subshell so it belongs to d-block elements.
For d-block elements group number
=no of electrons in (n-1) d subshell+number of electrons in valence shell (i.e.ns) =7+2=9