Question

Write atomic number difference between $1^{st}$ alkali metal and alkali earth metal of $3^{rd}$ period of periodic table.

Answer 1

Answer: 9

$1^{st}$ alkali metal $Li$ $(Z=3)$
Electronic configuration of lithium $=1s^2,2s^1$
Alkali earth metal of $3^{rd}$ period $Mg$ ( $Z=12$ )
Electronic configuration of magnesium $\left[Ne\right]3s^2$
The atomic difference between $1^{st}$ alkali metal and alkali earth metal of $3^{rd}$ period table: $=12-3=9$