The odd one out among the given options is option 'C', which represents the Electrostatic force.

**Viscous Force:**
- Viscous force refers to the resistance that a fluid (liquid or gas) exerts on an object moving through it.
- It is a type of frictional force that opposes the relative motion of the object and the fluid.
- Viscous force is responsible for phenomena like drag experienced by objects moving through a fluid medium.
- Examples of viscous force include the resistance experienced by a car moving through air or a boat moving through water.

**Frictional Force:**
- Frictional force is the force that opposes the motion or attempted motion of an object past another object with which it is in contact.
- It arises due to the roughness or irregularities present on the surfaces in contact.
- Frictional force plays a crucial role in our daily lives, such as walking, driving a car, or holding objects.
- It can be both advantageous (e.g., walking) and disadvantageous (e.g., wearing out of machine parts).

**Electrostatic Force:**
- Electrostatic force is the force of attraction or repulsion between charged objects.
- It arises due to the electric charge carried by the objects.
- Objects with the same charges repel each other, while objects with opposite charges attract each other.
- Electrostatic force is responsible for various phenomena such as the attraction of clothes after being dried in a dryer or the repulsion of two magnets.

**Air-Resistance:**
- Air resistance, also known as drag, is a force that opposes the motion of an object through the air.
- It is caused by the collision of air molecules with the object in motion.
- Air resistance depends on factors such as the shape and size of the object, the speed of motion, and the density of the air.
- It affects objects moving through the air, like a falling parachute or a moving car.

**Explanation:**
The odd one out is electrostatic force because it is the only option that does not involve the interaction between objects in motion or with a fluid medium. Electrostatic force is related to the interaction between charged objects, whereas the other three forces (viscous force, frictional force, and air resistance) are associated with the motion of objects through a medium (fluid or air).

A,B and D are the opposing forces but the C is not an opposing force