Name two solid, two liquids and two gaseous elements at the room temperature.

Which of the following substances are elements?

Water, Salt, Mercury, Iron, Marble, Diamond, Wood, Nitrogen, Air, Graphite, Hydrogen, Oxygen, Sugar, Chlorine

State three reasons why you think air is a mixture and water is a compound.

Explain why, hydrogen and oxygen are considered elements whereas water is not considered an element.

What are the three groups into which all the elements can be divided? Name two elements belonging to each group.