Question

use practical theory to explain why solids and liquids cannot be compressed(squashed into a smaller volume)?

Answer 1

Solids and liquids both have molecules. The molecules in solid are very close to each other. So it cannot be compressed easily. Hence, due to strong force of attraction they do not flow. Where as in liquids the situation is same but the particles are not much close and they forces of attraction is less. Hence they flow easily.