A typical thermos bottle has a thin vacuum space between the shiny inner flask (which holds a liquid) and the shiny protective outer flask, often stainless steel. The vacuum space is excellent at preventing :
i. Conduction
ii. Convection
iii. Radiation
iv. Conduction and Convection
v. Conduction, Convection and Radiation

iv. Conduction and Convection

Explanation:

A vacuum based thermos is excellent at containing the heat of the liquid without using any other techniques or excess energy. Hot liquid cools down by expelling the heat out and cool liquid heats up by taking in the heat form surrounding.

This heat transfer can take place through the process of conduction, convection and radiation. For conduction and convection a medium is required. Thus by creating a vacuum (absence of any medium), between inner and outer flask, conduction and convection are cancelled out thus stopping the heat transfer.

Still, heat transfer can occur due to radiation, which is cancelled out using shiny/reflective material.

a. are