Question

The correct electronic configuration of calcium(Atomic no. - 20) is :

• A. $2,7,8,3$
• B. $2,8,8,2$
• C. $1,8,8,3$
• D. $1,7,8,4$

Answer 1

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

Atomic number of calcium is 20. Number of protons = number of electrons = 20

First shell can accommodate 2 electrons so $K=2$.

Second shell can accommodate maximum of 8 electrons so $L=8$.

Third shell can accommodate maximum of 18 electrons but if we put remaining 10 electrons it will violate the law that outermost electron can accommodate 8 electrons so it will accommodate only 8 electrons.

So number of electrons in M is 8. Now the remaining two will be in N.

So the configuration is $2,8,8,2$