How to remove black marks in face which resulted due to acne and pimples?

Depends on the marks: Acne is caused by skin pores being plugged by tiny clumps of skin cells (the clump is called a comedone). When there are no bumps or actual pimples and pustules, the acne-prone areas of skin will still have plugged pores. Maybe the black spots are comedones in the skin pores. Dark spots can also be "post-inflammatory hyperpigmentation" that takes months to fade after pimples break and heal up.