Two rooms are in contact. one is at 15°c and the other at 21°c. choose the best statement concerning the heat flow.
a) heat will flow from the 21°c room to the 15°c room.
b) heat will flow from the 15°c room to the 21°c room.
c) there will be no exchange of heat.
d) heat will flow both ways in equal amounts.

The correct answer to the question is A). Heat will flow from the 21°C room to the 15°C room.

EXPLANATION:

Before coming into any conclusion, first we have to understand the direction of heat flow.

As per the second law of thermodynamics, heat will always flow from a body at high temperature to a body at low temperature unless and until external work is done.

As per the question, there are two rooms. One room is at 21 degree celsius while other one is at 15 degree celsius.

Hence, the room having 21 degree celsius is at high temperature than the room having temperature of 15 degree celsius.

Hence,  heat will flow from the 21°C room to the 15°C room.