1What is a molecule? Write the difference between an atom and a molecule.
2Which atoms are present in one molecule of water, and in what numbers?
3What is a compound? Write the difference between an element and a compound.
4Explain the relationship between element, molecule and compound using the figure given.
5Why does a compound not have the properties of the elements that made it? Give two examples.
6What does the phrase in a definite proportion mean in the definition of a compound?
7If there are only 118 elements, how can there be so many different substances in nature?
8Which is a molecule of an element and which is a molecule of a compound: O₂, H₂O, Cl₂ and HCl?
9Explain how a molecule keeps all the properties of the substance, using sugar as an example.
10Give the reason: hydrogen and oxygen both take part in burning, yet water puts out fires.