The word "unblemished" most nearly means "flawless".
Something that is unblemished is without any flaws or imperfections. It is perfect or complete.
The other options do not have the same meaning as unblemished.
- "Impaired" means damaged or made worse.
- "Sporadic" means happening irregularly or infrequently.
- "Unorthodox" means not conforming to the traditional or accepted way of doing things.