The atomic number of an element 'X' is 20.Write (a)its valency (b)whether it is a metal or a non-metal, (c)the formula of compound formed when the element 'X' reacts with an element 'Y' of atomic number 8. Justify your answer in each case

The element with atomic number 20, has electronic configuration   1s^₂ ,2s^₂ ,2p⁶,3s^₂ ,3p⁶,4s².

So, its valency will be 2. As there are two electrons in the outermost shell, it can loose them and attain argon configuration.

It is a metal. As it can loose electrons easily.

 

Y has atomic number 8, so electronic configuration will be  1s² ,2s² ,2p⁴. So, it needs two more electrons to fulfill the octet. The valency of Y is two.

 

As the valency ofsboth the element is 2, they will form the compound XY on reaction.