One part of the sentence has an error. Choose that part:

The correct answer is Option (2) → superior than Byron

Comparatives ending in -or:

• Adjectives taken from Latin such as superior, inferior, senior, junior, prior are followed by "to", not "than".
• This sentence: "superior than Byron" should be "superior to Byron".
  Corrected: Shelley is superior to Byron in his vision of democracy.
  Example: This cloth is superior to that one in quality.

Why the Other Options are Incorrect?

Option 1: Shelley is — Incorrect. The singular subject "Shelley" takes "is"; there is no error.

Option 3: in his vision — Incorrect. "In" correctly names the respect in which one poet is superior.

Option 4: of democracy. — Incorrect. "A vision of democracy" is the correct preposition.