Write two reasons responsible for the late discovery of noble gases.

Arrange the following elements in increasing order of their atomic radii.
$(a)$ $Li, Be, F, N$
$(b)$ $Cl, At, Br, I$

Define Newlands' law of Octaves.

An element $X$ which is a yellow solid at room temperature shows catenation and allotropy. $X$ forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are the major air pollutants.
$(a)$ Identify the element $X$
$(b)$ Write the electronic configuration of $X$
$(c)$ Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals?

Write true or false for the statement: It was assumed by Newlands that only $63$ elements existed in nature and no more elements would be discovered in the future.

If an element $X$ is placed in group $14$,what will be the formula and the nature of bonding of its chloride?