I have a thermal flask in which i have to fill the boiled water. I also have thermocol, saw dust and silver paper. Now tell me how i have to arrange these material to attain minimum heat loss.

In this case heat is flowing from flask to surrounding. So arrange materials in decending order of thermal resistance. i.e. poorest conducter of heat first.

that means the material with poorest conductor of heat should be placed first.. is that right...

As thermal condutivity of silver is more than sawdust and thermal conductivity of saw dust is more than thermocol, arrangement is like this..

Thermal flask, outside silver paper, outside saw dust and finally thermocol.

The materials shall be placed in increasing order of their convective heat
transfer coefficient viz thermocol, saw dust, and then steel, which has the
highest heat transfer coefficient.

Please tell me if i am wrong.

We need a material which has got lowest thermal conductance inside, which is in contact with the boiled water..so from inside first come silver paper, thermocol sawdust.