If the diameter of the capillary is doubled, the height of the water surface rising in it remains the same; option [C]. This is governed by the capillary action phenomenon described by the Jurin’s Law. According to this law, the height to which a liquid rises in a capillary tube is inversely proportional to the diameter of the tube. Therefore, doubling the diameter would result in halving the height, and vice versa. However, if the diameter is doubled, the effect cancels out, and the height remains unchanged. This principle is essential in various fields such as fluid mechanics, biology, and materials science, where capillary action plays a crucial role in phenomena like plant water uptake, ink absorption in paper, and the functioning of microfluidic devices. Understanding this relationship between capillary diameter and height helps in designing and optimizing systems utilizing capillary action for various applications.