The oil rises in the lamp wick due to capillary phenomenon; option [B]. The wick’s fibers act as tiny tubes, creating capillary action. This action draws the oil upwards against gravity, allowing it to reach the flame, where it vaporizes and burns. This process sustains the lamp’s flame by providing a continuous supply of fuel.

While pressure difference and low viscosity of oil are factors influencing fluid movement, they are not the primary reasons for oil rising in the lamp wick. Similarly, the presence of carboxylic groups in the oil does not directly contribute to its capillary rise. Instead, it’s the capillary action resulting from the wick’s structure and the cohesive and adhesive forces between the oil and the wick fibers that enable the oil to travel upward, facilitating the lamp’s functionality.