Question

What is the electronic configuration of calcium [$p=20,n=20$]?

• A. $2,8,8,1$
• B. $2,8,8,3$
• C. $2,8,8,2$
• D. $2,8,10$

Answer 1

The correct option is C $2,8,8,2$

Atomic no.$=$ no. of protons $=$ no. of electrons $=$ $20$
Mass no. $=$ no. of protons + no. of neutrons $=20+20=40$
K shell can accommodate $2$ electrons. L shell can accommodate $8$ electrons, N shell can accommodate $8$ electrons and the remaining $2$ electrons will be in M shell. Hence, the electronic configuration will be $2,8,8,2.$