One litre of water at 30 ⁰C is mixed with one litre of water at 50 ⁰C. The temperature of mixture will be ______________.

The correct option is D Between 30 ⁰C and 50 ⁰C

• Heat always flows due to temperature differences and flows from a body at high temperature to a body at low temperature.
• In this case, the heat will flow from water at 50 ⁰C to the water at 30 ⁰C.
• During this process of heat transfer, the temperature of the cold water will increase and the temperature of the hot water will decrease.

Hence, both hot and cold water will reach equilibrium temperature somewhere in between 30 ⁰C and 50 ⁰C.