Question

define valency and atomic size

Answer 1

Combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with is called valency.

Atomic size is the distance from the nucleus to the valence shell where the valence electrons are located. 
hope it helps u!!

Answer 2

valency is the combining capacity of an element

atomic size:- the bonding atomic radius is defined as one half of the distance between bonded nuclei