Which of the following element has two electrons in Q shell in its ground state?
Which of the following element has two electrons in Q shell in its ground state?
$\mathrm{Ba}$
$\mathrm{Ra}$
$\mathrm{La}$
$\mathrm{Pb}$
Solution
Q shell $\Rightarrow \mathrm{n}=7$ indicates the position of the element in period 7 in the periodic table.
$\mathrm{Ra}$ : electronic configuration $=4 \mathrm{~s}^2$ (valence shell $)$