Four possible Lewis diagrams for sulfur dioxide, SO₂, are given below. Which diagram best satisfies the electron-count, octet, and formal-charge criteria?
I. O=S=O (all atoms have two lone pairs; no formal charges)
II. O–S≡O (terminal O with two lone pairs; central S with one lone pair; +1 on S, –1 on singly bonded O)
III. O=S–O⁻ (terminal O on right with three lone pairs and –1; +1 on S)
IV. O–S–O (each O with three lone pairs; S with two lone pairs; no formal charges shown)
a) II
b) IV
c) III
d) I