Question

we can move our hand freely in air but not in sand and water

Answer 1

Because of friction..Air gives much less friction as compared to water and sand..So moving our hand in sand or water is much harder..

Answer 2

This is bcz particles of gas has the highest molecular spaces. Due to these spaces we are able to move our hand in bw the particles of air. In the case of sand and water, the particles have lower molecular spaces as compared to air.