Test: Modern Periodic Table of Elements - Class 10

The electronic structure of the noble gases is the basis for explaining why they are so unreactive.

On moving from left to right in a period, the chemical reactivity of elements first decreases and then increases.

On moving from left to right in a period, the number of valence electrons increases from 1 to 8.

On moving from left to right in a period, the atomic size decreases; the size of the atoms decreases.

X = Mg

Because Mg has valency 2 and valency in a group remains the same.

When Mg combines with chlorine it forms MgCl2.

Nonmetals are present on the right hand side of the periodic table. They are usually solids or gases at room temperature with low melting and boiling points (boron and carbon are exceptions). The only liquid non-metal is bromine. Most non-metals are brittle and are neither malleable nor ductile. 

All the Noble gases are placed in the group 18 and all elements are placed in the order of increasing atomic number. Therefore, the elements of atomic number before the Noble gas is placed in the before group of the period of Nobel gas which is group 17.