What is the maximum number of electrons that can occupy a $\mathrm{d}$ sublevel?

Which of the following elements can be classified as metalloids?

I. $\mathrm{Al}$    II. $\mathrm{Si}$    III. $\mathrm{Te}$

Which of the following elements are alkaline earth metals?

I. $\mathrm{Rb}$   II. $\mathrm{Sr}$   III. $\mathrm{Ba}$

What happens when sodium is added to water?

I. A gas is evolved.

II. The temperature of the water increases.

III. A clear, colourless solution is formed.

Which oxides produce an acidic solution when added to water?

I. ${\mathrm{P}}_4{\mathrm{O}}_{10}$   II. $\mathrm{MgO}$   III. ${\mathrm{SO}}_3$.

Which statement about the elements in group $17$ is correct?