Question

An element with an atomic no. Of _____ form basic oxide

Answer 1

$\bf{Z\:-\:12;\:Name\:-\:Magnesium}$

Well,there are many examples.

Any Element with < 4 valence electrons will donate them and hence will be called a metal.

Metals always form Basic Oxides.
Though there are some exceptions.

So, any element having < 4 valence electrons will form Basic Oxide.