Concept: Covalent bonds are formed by the overlapping of atomic orbitals. The type of overlap depends on the specific orbitals involved in the bonding.

Why (C) is correct:

Fluorine (F) is an element in Group 17 with atomic number 9. Its electronic configuration is $1s^{2}2s^{2}2p^5$. To achieve a stable octet, each fluorine atom needs one more electron. In the formation of a fluorine molecule ($F_2$), two fluorine atoms share their unpaired electrons. The unpaired electron in each fluorine atom resides in a 2p orbital. Therefore, the covalent bond in $F_2$ is formed by the axial (head-on) overlapping of the half-filled 2p orbital of one fluorine atom with the half-filled 2p orbital of another fluorine atom. This is a $p-p$ overlap.

Option Analysis:

• A) due to $s-s$ overlapping: This type of overlap occurs in molecules like $H_2$ where each hydrogen atom has an unpaired electron in its 1s orbital. Fluorine does not use s orbitals for bonding in $F_2$.
• B) due to $s-p$ overlapping: This type of overlap occurs in molecules like $HF$ where the 1s orbital of hydrogen overlaps with the 2p orbital of fluorine. It is not applicable for $F_2$.
• C) due to $p-p$ overlapping: Correct. The bond in $F_2$ is formed by the overlap of the 2p orbitals of two fluorine atoms.
• D) due to $d-d$ overlapping: This type of overlap involves d orbitals and is typically seen in elements from the third period onwards (e.g., in some transition metal complexes or elements like chlorine, bromine, iodine when forming multiple bonds or in hypervalent compounds). Fluorine does not have d orbitals in its valence shell.

Correct Answer: (C)