When is there a risk that the front wheel of the motorbike will lose contact with the carriageway?

You answered correctly. The front wheel of a motorbike can lose contact with the road when you accelerate in a low gear or when you accelerate while carrying a pillion passenger. In both situations, the weight shifts to the rear of the motorcycle, making it more likely for the front wheel to lift off (a "wheelie"). Braking with the front-wheel brake, on the other hand, transfers weight forward and increases contact, so it does not cause the front wheel to lose contact with the carriageway. When faced with similar questions, remember that strong acceleration increases the risk of the front wheel lifting, especially with extra weight at the back.