Question

Which of the following elements has least number of electrons in its M shell?

• A. K
• B. Mn
• C. Ni
• D. Sc

Answer 1

The correct option is A K

M is the third shell, thus no. of electrons in third shell of various elements can be calculated as;
E.C of K( atomic no. 19) = $\left[He\right]3s^{2}3p^{6}4s^1$ ; no. of electrons in M shell $=8$
E.C of Mn( atomic no. 25) = $\left[He\right]3s^{2}3p^{6}3d^{5}4s^2$ ; no. of electrons in M shell $=13$
E.C of Ni( atomic no. 28) = $\left[He\right]3s^{2}3p^{6}3d^{8}4s^2$ ; no. of electrons in M shell $=16$
E.C of Sc( atomic no. 21) = $\left[He\right]3s^{2}3p^{6}3d^{1}4s^2$ ; no. of electrons in M shell $=9$
Therefore K has least no. of electrons in the M shell.