The part of the sun’s radiation that heats the solar cooker is [B] infrared ray. Infrared radiation is responsible for transmitting heat energy and is abundant in sunlight. Solar cookers are designed to capture and utilize this infrared radiation, converting it into heat energy to cook food. Unlike ultraviolet or optical rays, which may have other effects or wavelengths unsuitable for cooking, infrared rays are ideal for generating heat. Cosmic rays, on the other hand, are high-energy particles originating from sources beyond the solar system and are not directly utilized for heating solar cookers. Therefore, among the options provided, infrared rays from the sun are the primary source of heat that powers solar cookers, making [B] the correct answer for the part of the sun’s radiation responsible for heating them.