Question

Predict the possible atomic number(s) of an atom in which the third shell is incompletely filled and maximum 3 more electrons can be added in that shell?

• A. 15 and 18
• B. 15 and 25
• C. 15 and 27
• D. All the above

Answer 1

The correct option is C 15 and 27

Given that the third shell is incompletely filled and can accommodate maximum of three electrons, the possible options are;
$1s^{2}2s^{2}2p^{6}3s^{2}3p^3$
$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^7$
Thus, the possible atomic numbers are 15 and 27 respectively.