Select the option that can be used as a one-word substitute for the given group of words.
Too strong to be defeated or changed

Correct option is A

The correct one-word for the given group of words is (a) Invincible.

Invincible: Someone or something too powerful to be conquered, overcome, or defeated. (Hindi: अजेय, जिसे हराया नहीं जा सकता)
Example: The army appeared invincible after winning every battle without a scratch.

Meanings of the given other options:

• Option (b) Headstrong: Stubborn or determined to do as one pleases (जिद्दी)
• Option (c) Vigorous: Strong and full of energy (ऊर्जावान)
• Option (d) Sovereign: Supreme ruler or one with full authority (सर्वोच्च शासक)