Question

ice is kept in a double walled container why

Answer 1

double wall trap the air between double walled container .as air is bad conductor of heat it prevent ice from melting

Answer 2

A double wall container contains a vacuum between the two walls.

Vacuum has no air.

This therefor means there will be no heat transfer by convection.

The double wall is important because :

It prevents heat gain by the ice by convection and conduction hence keeping the ice in its state.