Question

Which of the following has the electronic configuration $\left[Kr\right]5s^2$?

• A. $Ba$
• B. $Ca$
• C. $Sr$
• D. $Rb$

Answer 1

The correct option is C $Sr$

The valence electrons are present in the $s$ orbital and the $s$ orbital is completely filled. Hence the element belongs to $2^{nd}$ group i.e. alkaline earth metal. The period number is $5^{th}.$
The element is strontium $\left(Sr\right)$.