Which of the following lists contain only elements?
a. air, iron, iodine, magnesium.
b. zinc, gold, aluminium, oxygen.
c. nitrogen, copper, mercury, water.
d. chlorine, argon, sodium, limestone.

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?