Oceanography and Hydrology

The demersal zone is the part of the sea/ocean/deep lake comprising the water column that is near to the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer of the larger profundal zone.

Option 4 is incorrect. All the above statements are correct.

Reason: Estuaries and lagoons are types of brackish water resources. Brackish water resources are those where sea-water and fresh water mix together. These resources serve important fish reservoirs. Marine fisheries include deep seas and coastline while freshwater fishes inhabit rivers and lakes e.g. Catla is a freshwater fish. 

Africa's coastline is relatively smooth compared to other continents, with fewer natural harbors and offshore islands. While there are some islands (like Madagascar, Zanzibar, Canary Islands), they are fewer compared to the numerous rivers, lakes near the Great Rift Valley, and coastal mountains like the Atlas and Drakensberg ranges. The phrasing 'not in good number' means 'relatively scarce'.

The Great Barrier Reef is the world's largest coral reef system, located off the coast of Queensland in northeastern Australia. It stretches over 2,300 km and consists of nearly 3,000 individual reefs and hundreds of islands formed by living coral polyps.

This is the correct option.

Yes, it is correct as salts dissolved in sea water increase the density and hence, it exerts more upward thrust.

The passage discusses how the water cycle transforms saltwater into freshwater. Converting means changing from one form, state, or function to another, which perfectly describes the transformation of saltwater to fresh water through evaporation and precipitation. The other options don't capture this transformative process.

Ocean currents are driven by three primary factors: Earth's rotation creates the Coriolis effect, wind patterns move surface water, and differences in water density (from temperature and salinity variations) cause vertical movement. Earth's revolution around the sun creates seasons but does not directly cause ocean currents. Therefore, only factors 1, 2, and 3 are correct.

A continental shelf is the submerged edge of a continent that gradually slopes from the shoreline to a drop-off point (usually around 200 meters deep), after which the sea floor slopes steeply down to the abyssal plain. It is NOT a mountain range, raised land, or plateau - those are terrestrial features. Option C accurately describes the gentle slope followed by steep descent characteristic of continental shelves.

The standard average salinity of seawater is 35 parts per thousand (ppt), often expressed as 35/1 or 35‰. This means 35 grams of salt per kilogram of seawater. The other values (27, 80, 42) don't match the established scientific standard for ocean salinity.

Tides are the rise and fall of sea level caused by the combined effects of gravitational forces exerted by the moon, sun and rotation of Earth.

If the Moon came closer to Earth, the gravitational pull on oceanic water would increase, causing higher tides. Tidal force is inversely proportional to the cube of distance, so a smaller distance means significantly stronger tidal effects. The temperature change (A), stopping of currents (B), and general sea level rise (C) are not direct consequences of the Moon's distance.

Sea depth is traditionally measured in fathoms in maritime navigation. One fathom equals 6 feet (approximately 1.83 meters). While meters are also used in modern contexts, fathoms remain the standard nautical unit for depth measurement on navigational charts. Feet and nautical miles are used for distance, not depth.