With respect to the potential of emitter, base and collector, a $\text{NPN}$ transistor conducts when

 

• A

  both collector and emitter are positive with respect to the base
• Correct answer
  B

  collector is positive and emitter is negative with respect to the base
• C

  collector is positive and emitter is at same potential as the base
• D

  both collector and emitter are negative with respect to the base

Solution

The transistor conducts in active state in which and input circuit is forward biased and output circuit is reversed biased

Hence, the correct answer is option: 'B'.