BOHEMIAN is the one word substitution for:

The correct answer is Option (1) → Unconventional life-style

Bohemian describes a person, often an artist or writer, who lives in an unconventional way, without caring for the usual rules of society. The word first meant a person from Bohemia; it came to mean a free, artistic way of living.
Example: The painter lived a bohemian life in a small attic full of canvases.

Why the Other Options are Incorrect?

Option 2: Orthodox attitude — Incorrect. Orthodox means following traditional, accepted beliefs. This is the opposite of a bohemian way of life.
Example: His orthodox parents did not approve of his long hair.

Option 3: Island Dweller — Incorrect. An island dweller is a person who lives on an island, an islander. Bohemian says nothing about where a person lives.
Example: Every island dweller depends on the ferry for supplies.

Option 4: Political advisor — Incorrect. A political advisor is a person who gives advice to a leader or party. It is a job, not a way of living.
Example: The minister asked his political advisor to draft the speech.