Question

how can we separate the mixture of sand and wood dust

Answer 1

if u you put both in water containing glass then sand will be at the bottom and the wood dust will be on the surface of the water
sand is more denser than the wood dust

Answer 2

@chmvijay I think you can better say that the sand is more dense than the water (so it will sink) and the wood dust is less dense than the water so it will float :)

Answer 3

i left that to think to the person who has asked question :)

Answer 4

@thomaster