Copper carbonate when heated turns:

1. Blue
2. Green
3. Black
4. Yellow

When lead acetate solution is added to potassium iodide solution a precipitate is formed which is:

1. Red
2. Yellow
3. White
4. Black

When sodium carbonate reacts with dilute hydrochloric acid, the gas evolved is:

1. Carbon dioxide
2. Nitrogen
3. Oxygen
4. Hydrogen

One of the conditions necessary for a chemical reaction to occur is :

1. Evolution of a gas
2. Physical contact between reactants
3. Change in colour
4. Formation of a precipitate