What should be the atomic number for an element to form an acidic oxide?

Consider the following radioactive decays

I. ${}_{92}\mathrm{U}{\stackrel{-\mathrm{\alpha }}{⟶}}_{90}\mathrm{Th}$ and

II. ${}_{90}\mathrm{Th}\stackrel{-\mathrm{\alpha }}{⟶}{}_{88}\mathrm{Ra}$

In which case group of parent and daughter elements remains unchanged.

Four elements W, X, Y, and Z have atomic numbers 12,18, 4, and 16:

Which of the above will form an acidic oxide?

The outermost subshell electronic configuration of an element is $3{\mathrm{d}}^5 4{\mathrm{s}}^2$.

Write the atomic number of the element.

An element $\mathrm{X}$ forms two oxides $\mathrm{XO}$ and ${\mathrm{XO}}_2$. The oxide $\mathrm{XO}$ is neutral but ${\mathrm{XO}}_2$ is acidic in nature.The element $\mathrm{X}$ is most likely to be