Assertion: Radar is used to detect an aeroplane in the sky.

Reason: Radar works on the principle of reflection of waves.

1. If both the assertion and the reason are true and the reason is a correct explanation of the assertion
2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion
3. If the assertion is true but the reason is false
4. If both the assertion and reason are false