If hot air rises, why is it cooler at the top of a mountain than near sea level ?

Why is clear night cooler than cloudy night ?

How does the time period of a simple pendulum change as it moved from from sea level to the top of a mountain ?

Why does sea water boil at higher temperature than normal water?

The speed of sound in humid air is more than in dry air, why? Will the speed of sound in humid hydrogen be more than that in dry hydrogen?

Biological Oxygen Demand or BOD increases with increase in water pollution. In this refernce, answer the questions that follows (i) At a particular segment of the river near a sugar factory, the BOD is much higher than the normal level. What is it indicative of? (ii) What will happen to the dissolved oxygen and living organisms in the part of the river?

Thermal conductivity of air is less than of felt but is a better heat insulator in comparison to air why?

Explain why a piece of metal feels cooler than a piece of wood in winter.