Question

solar cell is forward or reverse bias . Give answer with reason .

Answer 1

That being said, a solar cell is primarily (exclusively?) used to generate electrical power, which it does when in forward-bias mode. In reverse-bias mode it actually consumes power, which is provided by whatever power source is used for the reverse-bias. So reverse bias operation completely defeats the purpose of a solar cell.
As far as I know, solar cells operate with no bias. Both forward bias or reverse bias would defeat the purpose. They have an external load, and the built in field alone separates the electrons and holes.