A solution contains 40 ml of ethanol mixed with 100 ml of water. Calculate the concentration regarding volume by volume percentage of the solution.

Write the skeletal equation for the following reactions: (i) Hydrogen sulphide reacts with sulphur dioxide to form sulphur and water. (ii) Methane on burning combine with oxygen to produce carbon dioxide and water.

Illustrate with an example that physical and chemical changes can take place together?

Name the three carbon molecule that is formed due to the break-down of glucose during respiration.

Define a chemical reaction. Which observations help you to determine whether a chemical reaction has taken place?