Question

what is 2nsquare rule

Answer 1

it is rule used in chemistry to count no. of atoms in the element
in first shell 2n^2(n=1)

Answer 2

Hey, here is your answer --

$2n {}^{2}$
rule is used to find the number of complete electron in each shell of atom

like , K shell = 2 $\times 1 {}^{2}$

L shell = 2 $\times 2 {}^{2} = 8$

hope u like it