Question

add lone pairs to compound a.

Explanation:

Step1: Determine valence electrons of S

Sulfur has 6 valence electrons.

Step2: Count bonded electrons per S

Each S forms 2 bonds (1 to another S, 1 to C), so 4 electrons used in bonding.

Step3: Calculate lone pair electrons per S

Lone pair electrons = $6 - 4 = 2$ pairs per S.

Step4: Add lone pairs to each S

Each sulfur atom gets 2 non-bonding electron pairs.

Answer:

The final structure has two lone electron pairs on each sulfur atom, resulting in the structure:

     H     H
     |     |
H - C - S - S - C - H
     |     |
     H     H
     (each S has two pairs of dots: :S-S:)

Visually, each sulfur will have two sets of two dots (lone pairs) attached to it, fulfilling the octet rule.