Question

The total number of electrons having n+l=3 in kr atom

Answer 1

Atomic number of Kr = 36

Its electronic configuration : $1s^{2},2s^{2},2p^{6},3s^{2},3p^{6},3d^{10},4s^{2},4p^{6}$

In n+l=3, n denotes the principal quantum number and l denotes the azimuthal quantum number  

The azimuthal quantum number values for all orbitals

s = 0, p = 1 , d = 2, f = 3

means following combinations are possible which has n+l=3

3s^{2} , electrons = 2

2p^{6} , electrons = 6

So, only 8 electrons in 2p^{6},3s^{2} has n+l=3 in Kr