Didwana, Kuchaman, Sargol and Khatu are all names of saline lakes located in India.

Option 1, glaciers, is incorrect as these names do not correspond to any known glaciers in India.

Option 2, mangrove areas, is also incorrect. Mangroves are typically found in tropical and subtropical regions, along coastlines and estuaries. None of these places are known for their mangrove ecosystems.

Option 3, Ramsar sites, is not applicable. The Ramsar Convention is an international treaty for the conservation and sustainable use of wetlands and Ramsar sites are wetlands deemed to have international importance. However, these lakes are not listed as Ramsar sites.

Thus, option 4, saline lakes, is the correct answer. These names belong to saline lakes found primarily in the thar desert region of Rajasthan, India. Saline lakes are bodies of water that have a high concentration of salts, often making the environment too harsh for most organisms. These specific saline lakes are important landmarks typically used for salt production.