Correct Answer: Unusual

Solution : The first option is correct.

Peculiar describes something distinctive or particular in an individual or group, often in a way that is perceived as strange or odd. Similarly, unusual signifies something not commonly encountered, out of the ordinary, or exceptional.

The meanings of the other options are as follows:

• Customary means according to the customs or practices; usual.
• Perplexed means confused, bewildered, or puzzled.
• Proven means demonstrated or established as true or reliable.

Therefore, the correct answer is unusual.