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 :

Answer: A. Hydrogels are used in controlled drug delivery only (statement 1). Hydrogels are three-dimensional polymer networks that absorb large amounts of water while remaining structurally stable. Their tunable porosity and biocompatibility make them ideal for medical applications. (1) Controlled drug delivery: YES. Hydrogels release drugs at predictable rates in response to pH, temperature or enzymes. Used in cancer therapy, wound dressings, contact lenses. (2) Mobile air-conditioning systems: NO. Mobile A/C uses refrigerants (HFCs, CO2) and compressors, not hydrogels. Confusion may arise with desiccant cooling but standard automobile A/C does not use hydrogels. (3) Industrial lubricants: NO. Lubricants are oil-based or synthetic; hydrogels are water-swollen polymers and lack the friction-reduction properties needed. Source: CSIR-Indian Institute of Chemical Technology hydrogel research papers / standard polymer engineering texts.