The number of atoms present in a molecule of water is:

1. 2
2. 3
3. 4
4. 5

What does 2H represent ?

1. two atoms of hydrogen
2. two molecules of hydrogen
3. one molecule of hydrogen
4. none of the above

Which of the following sets of elements are present in the same group of the Periodic Table ?

1. sodium, magnesium
2. beryllium, boron
3. oxygen, sulphur
4. carbon, nitrogen

Which of the following is a non-metallic polyatomic cation ?

1. nitrate ion
2. ammonium ion
3. aluminium ion
4. chloride ion