Pointing to a photograph a lady tell Mohan, ?I am the only daughter of this lady and her son is your maternal uncle.? How is the speaker related to Mohan?s father?

Explanation Option [a] is correct. The lady who is speaking is the only daughter of the lady in photograph. The son of the lady in photograph is the brother of lady who is speaking. If the brother of the lady speaker is the maternal uncle of Mohan, then the lady speaker is the mother of Mohan, and so she is also the wife of Mohan's father.