Question

write the scientific reason​

Answer 1

across a period the atomic radius decreases because of increase in nuclear charge

atomic radius increases down a group

valency is same in a group

and increases and again decreases across a period

Answer 2

In modern periodic table elements are arranged in increasing order of atomic no. thus as we go left to right in period no. of shell remain constant but no. of electron increase one by one and down a group no. of valance electron remain same but shell is increase one by one