Which of the following has a melting point greater than room temperature?
a. oxygen
c. iron
b. water
d. bromine

Technically, the answer is iron. Oxygen has a melting point way below zero (-219 degrees celsius), ice becomes water AT room temperature and bromine is already a liquid at room temperature. So, iron has a melting point greater than room temperature due to the fact that metals are made up of giant structures of atoms in a regular arrangement, and there are strong forces of electrostatic attraction between positive metal ions and negative electrons, meaning that a lot of heat energy is required to break the bonds, i.e. a very high melting point, approx. 1500 degrees celsius. Hope this helps.

Iron has a melting point greater than room temperature, as its particles are arranged. 

It changes food into energy that the organism can use.