Use the idea of a thermos flask to explain conduction, convection and radiation. Comment also how a thermos flask can reduce heat loss.

Conduction is the transfer of heat caused by the collision of particles inside a substance and between substances. In order to reduce heat loss, some thermos flasks have a vacuum between the container of the substance and the outside part of the flask, so no collisions can happen and no heat is lost.
Radiation is the emission of an electromagnetic wave due to the excited state of an atom. Except when the atom is at absolute 0, it will emit radiation. In order to prevent heat loss from this electromagnetic wave, thermos flasks are reflective inside, so all radiation is reflected inside flask.
Convection is the flow of heat due to the movement of a substance relative to its source. The air can only move within the thermos flask, because it is air tight, so it will not affect as a source of heat loss.