The electronic configuration of an element $\mathrm{T}$ is $2$,$8$,$7$. How many valence electrons are there in an atom of $\mathrm{T}$?

The electronic configuration of an element $\mathrm{T}$ is $2$,$8$,$7$. Is it a metal or a non-metal?

Name or state the following with reference to the elements of the first three periods of the periodic table:

A metalloid in Period $3$.

Name or state the following with reference to the elements of the first three periods of the periodic table:

The group whose elements have zero valency.

Name or state the following with reference to the elements of the first three periods of the periodic table:

The electrovalent compound formed between an alkaline earth metal and a halogen.