A thermos (vacuum) flask keeps liquids hot or cold for long periods by employing several design features. State which mode of heat transfer is chiefly reduced by each of the following features:
(i) silvered inner surfaces of the glass walls,
(ii) the evacuated space between the double walls,
(iii) a cork or plastic stopper at the mouth of the flask.
a. (i) silvered inner surfaces
b. (ii) evacuated space
c. (iii) cork or plastic stopper