Q.

Assertion: Dark phase is independent of light, hence called light independent phase.
Reason: Dark phase takes place at night.

1 Both assertion and reason are correct and reason is the correct explanation of assertion.  
2 Both assertion and reason are correct but reason is not the correct explanation of assertion.  
3 Assertion is true but Reason is false.  
4 Assertion is false but Reason is true.  

Ans.

(3)

Dark phase is also known as light independent phase, unlike light phase, it does not require light as an essential factor, thus can take place both in the presence and absence of light.