Question

The ratio of number of electrons in N shell of A and M shell of B with atomic numbers 40 and 32 respectively is
(1) 5 : 3
(2) 9 : 5
(3) 5 : 9
(4) 5 : 4

Answer 1

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Electronic configuration for A = 2,8,14,9

Electronic configuration for B = 2,8,14,9

Atomic number of A = 33

Atomic number of B = 33

Ratio of their Atomic Masses = 33 / 33

= 1 : 1

Answer 2

The answer of this question is 2:3

Sol:- First write the electronic configuration of atomic no. 40 or element A

1s^2,2s^2,2p^6,3s^2,3p^6,4s^2,3d^10,4p^6,5s^2,4d^2

Now as the ques says in N shell which means 4th one so,we will add the powers of4s^2,4p^6,4d^2 i.e 2+2+6 =*10* Similarly do the next part and add the powers of all those starting with the no. 3 which comes out to be* 15 * .....The the ratio is 10/15or2/3.......