Which of the following adaptations help aquatic plants to float in water?

The correct option is B Air spaces in the stem and other plant parts.
The air spaces in stem and other parts of aquatic plants keeps them afloat in water by reducing the mass of the plant. Presence of waxy coating on the leaf surfaces prevents the leaves from decaying in water. Most of the aquatic plants have poorly developed root system. Some aquatic plants have submerged stems and their roots anchored to the soil. Few aquatic plants have roots that are very short and fibrous. These plants are entirely afloat.