Filtration:
Filtration is a process used to separate solid particles from a liquid or gas by passing it through a filter. It is not suitable for separating a mixture of wheat and husk because both wheat and husk are solid particles and cannot be separated by this method.

Decantation:
Decantation is a process used to separate a mixture of liquid and solid particles by pouring off the liquid while leaving the solid particles behind. In the case of a mixture of wheat and husk, decantation is not suitable because both wheat and husk are solid particles and cannot be separated by pouring off the liquid.

Sieving:
Sieving is a process used to separate particles of different sizes by passing them through a sieve or mesh. It is the most suitable method for separating a mixture of wheat and husk. Wheat grains are larger in size compared to husk particles, so when the mixture is passed through a sieve, the husk particles will be retained on the sieve while the wheat grains will pass through. This allows for the separation of wheat and husk.

Evaporation:
Evaporation is a process used to separate a mixture of a solid and a liquid by heating it to convert the liquid into vapor, leaving behind the solid. It is not suitable for separating a mixture of wheat and husk because both wheat and husk are solid particles and cannot be separated by this method.

Therefore, the correct answer is option 'C' - sieving. Sieving is the most appropriate method for separating a mixture of wheat and husk as it takes advantage of the difference in particle sizes between the two components.