Which of the following is an example of contact force?

Muscular force

The correct answer is option 2. Muscular force.

Contact forces are interactions between objects that occur when the objects are physically touching each other. These forces arise due to the interaction of the surface molecules of the objects involved. Unlike non-contact forces, which act over a distance without direct contact between the objects, contact forces require direct physical contact for their effects to be observed.

"Muscular force" is an example of a contact force because it occurs when muscles physically come into contact with an object and exert a force on it. For example, when you push a door open, lift a book, or pull an object towards you, you are exerting muscular force through direct contact between your muscles and the object. This force is transmitted through physical contact, resulting in a change in the object's motion or state.