In which of the following are hydrogels used? 1. Controlled drug delivery in patients 2. Mobile air-conditioning systems 3. Preparation of industrial lubricants Select the correct answer using the code given below:

Hydrogels are networks of polymer chains that are hydrophilic, meaning they are insoluble in water but can absorb large amounts of water (up to 99%) without dissolving. Their unique properties make them versatile for various applications: 1. **Controlled drug delivery in patients:** Correct. Hydrogels are extensively used in biomedicine as drug delivery systems. They can encapsulate drugs and release them gradually or in response to specific stimuli (e.g., pH, temperature), allowing for controlled and targeted drug delivery, minimizing side effects and improving therapeutic outcomes. 2. **Mobile air-conditioning systems:** Correct. Superabsorbent polymers, which are often hydrogels, can be used in desiccant-based air conditioning systems. These hydrogels absorb moisture from the air, thereby cooling it down. This application is particularly relevant for energy-efficient or mobile cooling solutions, including some experimental or niche air conditioning systems. 3. **Preparation of industrial lubricants:** Correct. Hydrogels can be incorporated into lubricants to modify their rheological properties (flow and deformation) and enhance their performance, especially in aqueous-based or specialized lubrication applications. Their water-absorbing and retaining properties can be beneficial in certain lubrication contexts, such as reducing friction and wear. Therefore, hydrogels can be used in all three listed applications.