Question

Observe the following molecules: ClF, SF$_4$, CH$_4$, NH$_3$, XeF$_4$, PCl$_5$. The number of molecules in which the central atom has expanded octet is:

• A. 6
• B. 4
• C. 5
• D. 3

Hint:

An expanded octet occurs when the central atom has more than 8 electrons, typically in elements from the third period or beyond (e.g., S, P, Xe).

Answer 1

The Correct Option is D

Expanded octet means the central atom has more than 8 electrons in its valence shell (possible for elements beyond the second period).
ClF: Cl has 7 electrons, 1 bond, no expanded octet (8 electrons).
SF$_4$: S has 10 electrons (4 bonds + 1 lone pair), expanded octet.
CH$_4$: C has 8 electrons, no expanded octet.
NH$_3$: N has 8 electrons, no expanded octet.
XeF$_4$: Xe has 12 electrons (4 bonds + 2 lone pairs), expanded octet.
PCl$_5$: P has 10 electrons (5 bonds), expanded octet.
Number of molecules with expanded octet = 3 (SF$_4$, XeF$_4$, PCl$_5$).