Because of convection, the warmest air in a room
a. spreads out in all directions.
b. rises toward the ceiling.
c. transfers heat to the walls.
d. sinks toward the floor.

The correct choice is
B. rises toward the ceiling
In fact, the warmest air is also the air with least density: in warm air, the particles move faster, so the distance between them is larger, on average. Therefore, the warmest air is less dense, and because of that it tends to flow upwards (due to Archimede's principle) and it is replaced by the colder air, creating the so-called convection current.