The incorrect statement regarding conformations of ethane is:

Step 1: Recall conformational analysis of ethane

Ethane ($\ce{CH3-CH3}$) can rotate freely about the $\ce{C-C}$ $\sigma$ bond, giving rise to an infinite number of conformations.

Step 2: Evaluate each statement

(a) Ethane has infinite number of conformations — TRUE ✓ Free rotation about the $\ce{C-C}$ bond generates a continuous range of dihedral angles (0° to 360°).

(b) Dihedral angle in staggered conformation is $60°$ — TRUE ✓ In the staggered conformation, H atoms on adjacent carbons are 60° apart (the dihedral angle between any two H on opposite carbons).

(c) Eclipsed conformation is the most stable — FALSE ✗ The eclipsed conformation is the LEAST stable (highest energy) due to maximum torsional strain (electron repulsion between eclipsed bonds). The staggered conformation is most stable.

(d) Conformations are interconvertible — TRUE ✓ At room temperature, $\ce{C-C}$ bond rotation occurs readily ($\sim 12$ kJ/mol barrier), so conformers interconvert.

Step 3: Identify the incorrect statement

Option (c) is incorrect.

Key Points to Remember:

• Staggered conformation = most stable (minimum torsional strain)
• Eclipsed conformation = least stable (maximum torsional strain)
• Energy difference between staggered and eclipsed ethane ≈ 12.5 kJ/mol