Assertion (A) : Despite low evaporation and stable stratification of the atmosphere, salinity is high in polar regions. Reason (R) : Sea water freezes leaving the remaining water saline than before.

Assertion (A) is false because polar regions generally exhibit low surface salinity, typically ranging between 20 and 32 psu [4]. This is due to high freshwater input from melting ice and low evaporation rates [4]. While the atmosphere is cold, the ocean surface is often characterized by a 'lid' of lower salinity water that maintains stable stratification [2]. Reason (R) is true as it describes 'brine rejection' [5]. When sea water freezes, salt ions are excluded from the ice crystal lattice and forced into the surrounding water, increasing the salinity and density of the remaining liquid [5]. This process is critical for forming dense water masses like Antarctic Bottom Water [5]. However, because the overall net effect in polar regions (considering melting and precipitation) is freshening, the assertion that salinity is 'high' is incorrect [4].

Sources

1. [4] https://en.wikipedia.org/wiki/Brine_rejection
2. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 33: Ocean temperature and salinity > Atlantic > p. 519
3. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC9668305/
4. [5] https://pmc.ncbi.nlm.nih.gov/articles/PMC9759544/