Assertion: In optical fibre, the diameter of the core is kept small.
Reason: The smaller diameter of the core ensures that the fibres should have incident angle more than the critical angle required for total internal reflection.

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true but reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

Hi ! Studying late night...