Answer: d) Tropical regions with high evaporation rates

• • Explanation: In areas with higher evaporation, more water leaves behind its dissolved salts, leading to a higher concentration and increased salinity.

Answer: c) It increases as water leaves behind salts.

• • Explanation: Evaporation only removes water, leaving behind the previously dissolved minerals and increasing the concentration of salts.

Answer: a) Rainwater erosion of rocks

• • Explanation: Rivers carry dissolved minerals from land, but the continuous erosion of rocks by slightly acidic rainwater over vast areas contributes the most to ocean salinity.

Answer: d) Depth of the water column

• • Explanation: While deep ocean layers have slightly different mineral compositions, they're less affected by surface events like evaporation or freshwater input compared to shallower areas.

Answer: c) They remain dissolved and contribute to salinity.

• • Explanation: The water may evaporate, but the minerals remain part of the ocean's dissolved salt content.

Answer: c) Sodium chloride (table salt)

• • Explanation: Although other minerals are present, sodium chloride makes up about 85% of the dissolved salts in the ocean.