When we sit on a seat with rubber mattress or lie down on the mattress, its shape changes. Found in such a substance:

Option C: Stored energy is found in a substance like a rubber mattress when its shape changes as we sit or lie on it. In this context, the stored energy refers to elastic potential energy, which arises due to the deformation of the rubber material. When we apply force to the rubber mattress by sitting or lying on it, the material undergoes deformation, causing it to temporarily store energy within its structure. This stored energy is potential energy because it has the potential to do work or return to its original shape when the external force is removed. In the case of the rubber mattress, the stored elastic potential energy allows the material to exert a restoring force, attempting to return to its original shape, once the weight is removed. This property of rubber, known as elasticity, enables it to absorb and release energy, making it useful in various applications like shock absorbers, springs, and cushioning materials. Therefore, the correct answer is option C, stored energy, specifically referring to the elastic potential energy stored within the rubber material when its shape changes due to external forces.