We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert

We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert. 

Answer:- Since, air is gas, so its particles are loosely packed and there is negligible force of attraction between its particles. Because of that we can easily move our hand in air. 

But wood is a solid, so the force of attraction between its particles is greatest. The particles of wooden block are closely packed. That’s why we

cannot move our hand through a solid block of wood. 

However a karate expert can exert required pressure to break the great force of attraction of the particles of a solid wooden block.