Explanation: Heat developed within a storage cell under charge or discharge conditions is caused by two primary factors. Firstly, **I2R losses** (also known as Joule heating) occur because every component of the battery, including the electrolyte, plates, and terminals, has some electrical resistance (R). Whenever current (I) flows through this resistance, electrical energy is converted into heat. This is a fundamental principle of electrical circuits. Secondly, **energy transfer due to chemical reactions** contributes to heat generation. The electrochemical processes that store and release energy in a battery are not perfectly efficient. The chemical reactions themselves inherently release or absorb heat (enthalpy changes) as part of their thermodynamic profile, separate from any resistive losses. This intrinsic heat generation or absorption is a characteristic of the chemical transformations occurring within the cell. Therefore, both resistive losses and the thermodynamics of the chemical reactions contribute to the overall heat developed in a storage cell, making option C the correct answer.