Question

When hot drinks are stored in a vacuum flask, it is important to keep the stopper in the flask. Why is it less important to have a stopper in a flaks that is being used to kepp things cold? ​

Answer 1

beacause

(1) in first situation when the flask is open the are outside will go inside and the hot drink will start coolling by thr process of evaporation ....

(2)in second situation iif the cools drinks are kept inside the openflask no matter what happen the cool drinks will remain ..

it generally during winter but in summer you close it because as told before the hot air outside will go insode and hence it no more remains cool......