The bond angle in a molecule is primarily determined by the hybridization of the central atom and the number of lone pairs present. For molecules with no lone pairs on the central atom, the hybridization directly dictates the ideal bond angles.

Concept: Hybridization and Bond Angles

• sp hybridization: Involves one s and one p orbital, forming two sp hybrid orbitals. These orbitals are oriented at 180° to each other, resulting in a linear geometry. Example: C₂H₂.
• sp² hybridization: Involves one s and two p orbitals, forming three sp² hybrid orbitals. These orbitals are oriented at 120° to each other, resulting in a trigonal planar geometry. Example: C₂H₄.
• sp³ hybridization: Involves one s and three p orbitals, forming four sp³ hybrid orbitals. These orbitals are oriented at 109.5° to each other, resulting in a tetrahedral geometry. Example: CH₄.

Based on these ideal bond angles:

• Bond angle for sp hybridization = 180°
• Bond angle for sp² hybridization = 120°
• Bond angle for sp³ hybridization = 109.5°

Therefore, the correct order of bond angles from smallest to largest is sp³ < sp² < sp.

Option Analysis:

• A) sp 3 < sp < sp 2: Incorrect. This order is 109.5° < 180° < 120°, which is wrong.
• B) sp < sp 2 < sp 3: Incorrect. This order is 180° < 120° < 109.5°, which is wrong.
• C) sp 2 < sp < sp 3: Incorrect. This order is 120° < 180° < 109.5°, which is wrong.
• D) sp 3 < sp 2 < sp: Correct. This order is 109.5° < 120° < 180°, which is correct.

Correct Answer: (D)