The correct option is "1 only" because hydrogels are highly absorbent polymers that can swell in water and are primarily used in biomedical applications, particularly for controlled drug delivery systems. They can encapsulate drugs and release them in a controlled manner over time, significantly enhancing therapeutic efficacy and patient compliance. In contrast, mobile air-conditioning systems and industrial lubricants rely on different chemical properties and do not utilize the unique swelling and gel-like characteristics of hydrogels, which separates their application fields in the context of materials science and biomedical engineering.