When a few drops of water are sprinkled over hot oil, what makes it crackle and fizz?
Hot oil is very much hotter than the boiling point of water. When you put drops of water in hot oil, they sink in a little (water being heavier than oil) and then convert into steam that escapes with explosive force. That is the reason for the noise. Of course nothing like this happens if you pour a little oil on boiling water, for the obvious reason that oil stays near the surface and cannot be vaporised suddenly because the boiling water is just not hot enough. How do fish get the oxygen they need from water? Some oxygen is always dissolved in water. Fish extract it out using their gills. You must have noticed that in a home aquarium, a motor keeps blowing air into the fish tank; you can see the bubbles rising up. This is to oxygenate the water and keep it breathable that is for creatures with gills.
