What characteristic defines hydroscopic oil?

Hydroscopic oil is defined by its high attraction to moisture, which makes option B the correct choice. This characteristic is significant because hydroscopic oils are capable of absorbing water from the environment. This property can have implications for their use in refrigeration systems, as the presence of moisture in the oil can lead to various operational issues, including reduced lubrication efficiency, potential corrosion, and the creation of acids that can harm the refrigeration system components.

The other options, while they might describe some types of oils, do not accurately describe the essential attribute of hydroscopic oils. Low viscosity refers to the thickness or flow characteristics of a fluid, which is unrelated to its moisture absorption capabilities. High thermal conductivity pertains to the capability of a substance to conduct heat, which is not a defining trait of hydroscopic oils. Quick evaporating describes the rate at which a substance changes from a liquid to a gas, and this characteristic does not relate directly to moisture attraction. Therefore, the defining trait of hydroscopic oil is its high attraction to moisture.