The correct answer is option 1: Arabian Sea exhibits a high rate of evaporation and a low influx of freshwater. This means that the Arabian Sea experiences more evaporation of water compared to the Bay of Bengal, resulting in higher salinity levels. Evaporation occurs when water changes from a liquid to a gas, leaving behind the dissolved salts and minerals, thus increasing the concentration of salt in the sea water.

On the other hand, the Bay of Bengal is influenced by several large rivers, such as the Ganges, Brahmaputra, and Irrawaddy, which bring freshwater into the sea. This influx of freshwater helps dilute the salt content, resulting in lower salinity levels compared to the Arabian Sea.

Options 2 and 3 are unrelated to the salinity levels of the Arabian Sea. The depth of the water does not directly impact salinity, and the presence of more enclosed land does not necessarily affect evaporation or influx of freshwater.

Option 4 is incorrect because the Arabian Sea actually receives less rainfall compared to the Bay of Bengal. Higher rainfall would introduce more freshwater into the sea, potentially reducing salinity levels.

Overall, the high rate of evaporation and low influx of freshwater in the Arabian Sea contribute to its higher salinity levels compared to the Bay