To answer our asked question why are solids rigid ?
The states of any matter can be classified on the basis of intermolecular forces , On the basis of intermolecular forces of matter , solid is a type of matter. The solid is differ from other matter on basis of packaging of molecules.
In the solids , the constituent particles like atom ,molecule, ions are remain fixed , means they can’t move freely like other states of matter. But due to strong attraction force which is working between particles of matter / solid , they can oscillate on their own position. means they can oscillate only but can not move freely or can’t move from one place to another in the solids .
Because the solids have closely packed arrangement of constituent particles like atom ,molecule, ions , they are rigid in nature.
In short we can say solids particles have fixed or non movable arrangement of constituent particles , they are not free to move , they can only oscillate on their own position due to some force , because of these properties of solids are called rigid.