In an atom the number of electrons in M - shell is equal to the number of electrons in the K and L - shell . Answer the question.
Explanation :
1) Number of electrons in K-shell `(1 s^(2)) = 2`
Number of electrons in L-shell `(2s^(2) sp^(6)) = 8`
Total number of electrons in k & L shells = 10
2) Given that number of electrons in M-shell is equal to number of electrons in K& L- shells
3) Hence number of electrons in M-shell `(3s^(2) 3p^(6) 3d^(2)) = 10`
4) But , we know that before filling of 3d orbital 4s should be filled `(4s^(2))`
5) So , electronic configuration is `1s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(6) 4s^(2) 3d^(2)`

What is the atomic number of element ?

Explanation

The element is Ti (Titanium) . Its electronic configuration is `1 s^(2) 2 s^(2) 2 p^(6) 3s^(2) 3p^(6) 4s^(2) 3d^(2)`.