Consider the following statements about a thermos flask:

1. It is a practical device in which the heat flowing into or out of the system by conduction,convection or radiation is used as much as possible

2. It consists of a double walled glass vessel

3. The heat transfer by convection is minimised by silvering the surfaces and the radiation is minimised by evacuating the space between the walls

Which if the statements given above is/are true?

a) 1 and 2 only

b) 2 and 3 only

c) 1 and 3 only

d) 1, 2 and 3

Ans -[A]. 

Statement 3 is wrong. The heat transfer by radiation is minimised by silvering the surfaces and ctransfer of heat by onduction is minimised by evacuation space between the walls.