Why does an athlete breathe faster and deeper than usual after finishing the race?

Why does leather get hardened after tanning ?

Why does a sheet of paper fall slower than one that is crumpled into a ball?

In the experiment "light is essential for photosynthesis" why does the uncovered part of the leaf turn blue-black after putting iodine solution?

Why does the sun seem to rise two minutes before the actual sunrise and set minutes after the actual sunset ? Explain with the help of a labelled diagram.

Why does nitrogen show catenation properties less than phosphorus ?

Explain the following. a] Why is tungsten used almost exclusively for filament of electric lamps? b] Why are the conductors of electric heating devices, such as bread-toasters and electric irons made of an alloy rather than a pure metal? c] Why is the series arrangement not used for domestic circuits? d] How does the resistance of a wire vary with its area of cross-section? e] Why are copper and aluminum wires usually employed for electricity transmission?

State any one reason to explain why RNA viruses mutate and evolve faster than other viruses