In a convection current, why does cool air take the place of warmer air? 1.Cool air is denser than warm air, so it sinks to take the place of rising warm air.

2.Cool air is less dense than warm air, so it sinks to take the place of rising warm air.

3.Cool air is denser than warm air, so it rises to take the place of sinking warm air.

1.  Cool air is more dense than warm air so it sinks to take the place of the warm rising/buoyant air.

Explanation:

This is why heating a room with cold outside walls or glass windows (if budget can afford), we use warm radiant heaters at the floor level to break up the convection current/cold draft.  

As opposed to just diffusing air at the ceiling level, which is good in summer as cool air falls (air conditioning is in range of 55 to 65 degf out of the diffuser), mixing with warmer room air.

convex lenses are thicker at the middle. rays of light that pass through the lens are brought closer together (they converge). a convex lens is a converging lens. when parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.