What is a metalloid? Name any two of them.

$(a)$ What is the basis of arranging the elements in the Modern Periodic Table?
$(b)$ How does this remove the problem of positioning of isotopes?

State the reason for the following:
$(a)$ The elements of the same group have similar chemical properties.
$(b)$ The elements of the same period have different properties.

Two elements $X$ and $Y$ have atomic numbers $11$ and $16$ respectively.
$(a)$ Write the electronic configuration of both.
$(b)$ Which type of bond will they form?
$(c)$ Write the formula of the compound formed by their combination (in terms of $X$ and $Y$).

Atomic numbers of a few elements are given below: $10, 20, 7, 14$.
$(a)$ What would be the electronic configuration for each of these elements?
$(b)$ Determine the valency of these elements.

The order of increasing atomic size is: