i) Hot water is less dense and thus rises to the top due to convectional current.
ii) The liquid has reached its boiling point
iii) Heat losses are minimized as follows:
When 5oc below room temperature heat is gained; when 5oc above room temperature, the same amount of heat previously gained is now lost. Thus the net heat exchange is zero
Kavungya answered the question on May 31, 2019 at 10:03
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