Question

Can water be made to boil in a paper cup without the paper being burnt? If yes, then this is because _________________
(A) Temperature of water does not change during boiling.
(B) Ignition temperature of paper is higher than the boiling point of water.
(C) High latent heat of vaporization of water
(D) All of the above.

Answer 1

The difference of boiling point of water and the ignition point of paper are to be known to solve this question. Paper burns at a different temperature than boiling of water.

Complete step by step solution:
If a paper cup is held at a certain distance from the flame, then it can easily be used to heat some water in it. Water draws heat from a heat source by the method of convection until it reaches its boiling point of 100 $^0{\text{C}}$ . The temperature of the water remains fairly constant as it boils and gets converted into the gaseous state, because liquid water is incapable of getting hotter till it is converted to steam. Most papers burn at around 230 $^0{\text{C}}$ . As the water molecules draw heat from the surrounding paper, to get heated up by convection, it prevents the paper from getting heated too much and hence it does not reach its ignition point. Heat also escapes as steam that is formed from the liquid water.
Hence, it can be seen that all the above points are applicable. Hence, the correct answer is option D.

Note
Sand is another such substance like water that has the ability to conduct away heat from paper but it gets way hotter than water. When the temperature of sand crosses past 230 $^0{\text{C}}$ then the paper starts to burn.