Assertion (A) : It is easier to swim in sea- water compared to ordinary water. Reason (R) : Density of sea-water is higher than that of ordinary water.

The assertion that swimming in sea water is easier than in ordinary (fresh) water is true. This phenomenon is explained by the higher density of sea water compared to fresh water [t1][t2]. Sea water contains dissolved salts, which increase its mass per unit volume [t6][t8]. According to Archimedes' principle, the upward buoyant force exerted on an object is equal to the weight of the fluid it displaces [t9]. Because sea water is denser, a swimmer displaces a weight of water equal to their own body weight while submerging less of their volume compared to fresh water [t3][t5]. This increased buoyancy makes it easier to stay afloat and swim [t1][t7]. Therefore, the reason provided correctly explains why the assertion is true, as the higher density directly results in the greater buoyant force that facilitates easier swimming.

Sources

1. [1] https://www.noaa.gov/ocean/ll-eggs