Answer: Option (b) is the correct answer.
Step-by-step explanation:
When air is warmer then it means it molecules are moving rapidly from its initial place. Hence, its molecules gain more kinetic energy due to which there occurs more number of collisions between its molecules.
As a result, these molecules move farther apart from each other leading to the rise of air molecules.
Thus, we can conclude that the warm, moist air masses in the tropics rise in the atmosphere as they heat.