JEE Chemistry 2025 Question with Solution

Given: Element with atomic number $9$.

Find: Which among statements A, B, C, and D are correct.

Atomic number $9$ corresponds to Fluorine (F). Its electronic configuration is

Now evaluate each statement using the configuration above and Hund's rule.

For A: In $1s^2 2s^2 2p^5$, the spin distribution can be counted as $5$ electrons with $m_s = +\frac{1}{2}$ and $4$ electrons with $m_s = -\frac{1}{2}$. Therefore, statement A is correct.

For B: The $2p^5$ configuration means the three $p$ orbitals are occupied according to Hund's rule. Two orbitals become paired and one remains singly occupied. Hence it is not correct to conclude that there is only one electron specifically in $p_z$ orbital as a unique statement. Therefore, statement B is incorrect.

For C: The last electron enters a $2p$ orbital, so for that orbital

Therefore, statement C is correct.

For D: Angular nodes are equal to the azimuthal quantum number $l$. Thus,

So the sum of angular nodes of all the atomic orbitals present is

which is not $1$. Therefore, statement D is incorrect.

Hence the correct statements are A and C only. So the correct option is D.

Note: The solution marks option D, and option D corresponds to A and C Only.

Given: Atomic number $9$.

Find: The correct combination of statements.

Electronic configuration of Fluorine is

Orbital filling in the $2p$ subshell follows Hund's rule, so the electrons are distributed across three $p$ orbitals before pairing occurs.

• Statement A: True.
• Statement B: False.
• Statement C: True.
• Statement D: False.

Thus the correct set is A and C Only, which matches option D.