Why do the inner walls of a vacuum flask have a silver coating?
a) to stop heat loss by radiation
b) to reduce heat loss by radiation
c) to reduce heat loss by conduction
d) to reduce heat loss by convection

Answer:

The inner walls of a vacuum flask have a silver coating to reduce heat loss by radiation.

Explanation:

The vacuum flask has an inner silver lining to prevent the transfer of  heat by radiation. Radiation is a process where the emission or transformation of energy happens in the form of wave or the  particles through the material medium.

Vacuum flask being working as thermal insulator helps in maintaining the substance its actual temperature for a long time. The silver lining acts as a reflector .It  prevents the heat radiation to released out of the flask.  

that tool would be a compass