Given below are two statements based on the structures shown.

Statement I: B is more stable than A.

Statement II: Dihedral angle of B is more than A.

Choose the correct option.

The correct option is Both statement I and statement II are correct.

Let us analyze the two structures shown in the image:

Structure A: Represents the fully eclipsed conformation of butane. In this conformation, the two methyl (${\mathrm{CH}}_3$) groups on adjacent carbons lie directly behind one another. The dihedral angle ($\theta$) between the two methyl groups is:

$\theta =0°$

This structure experiences maximum torsional strain (due to eclipsing C-H and C-C bonds) and steric hindrance (due to the close proximity of bulky methyl groups), making it the least stable conformation.

Structure B: Represents the anti-conformation (staggered) of butane. In this conformation, the two methyl (${\mathrm{CH}}_3$) groups are positioned as far apart as possible. The dihedral angle ($\theta$) between the two methyl groups is:

$\theta =180°$

This conformation minimizes both steric hindrance and torsional strain, making it the most stable conformation of butane.

Now, let us evaluate the given statements:

Statement I: B is more stable than A.
Since staggered/anti conformations (B) have lower potential energy due to minimized steric and torsional strain compared to fully eclipsed conformations (A), conformation B is much more stable than conformation A. Thus, Statement I is correct.

Statement II: Dihedral angle of B is more than A.
The dihedral angle of conformation B is $180°$, and the dihedral angle of conformation A is $0°$. Since:

$180°>0°$

the dihedral angle of B is indeed greater than that of A. Thus, Statement II is also correct.

Therefore, both Statement I and Statement II are correct.