I don't have any idea for this question... "Explain the effect of surface area exposed to the air on the rate of cooling of hot water?:o"

Try imagining you have a dish of hot water, a cup of hot water and a thermos of hot water. All the volumes of water are the same, and the thermos is open. You'll see that the dish will have most surface area of water exposed to the air, then the cup, and lastly the thermos. Now, which do you think will cool down most rapidly?

If you can't see it this way, then try to think of evaporation. Evaporation is a process where water turns into a gaseous state, leaving behind less energetic molecules of water, so, the remaining water is cooler. Now, evaporation depends on what?

Hope those helped you figure out the required answer! :) Post back if you're not so sure.

Why imagine? Why not go and do the experiment? :)