Question A, B, D belongs to scope of physics such as in question A sound under the water travels in form of current and thus these currents are quite lower in deep water where the aquatic animal find stability in comparison to shallow water or near to the water surface where the current is higher.
In question B, speed of sound under the water can be caliberated by the concentration of the ions present in the water and thus higher the concentration greater will the speed of sound.
In C, the current of ocean is higher in summer due to the higher temperature and thus Question A, B, D belongs to scope of physics only C belongs to chemistry asking about the mixing of wastewater in river to increase acidity all relates to pH of water.
