Differentiate between the terms elements, compounds and mixtures. 

The important physical properties of substances are colour, odour, nature, density and solubility in water. Name -

a) two coloured gases (with their colours) 

b) a gas with a pungent, choking odour which is lighter than air

c) a poisonous gas almost as heavy as air. 

An atom of an element is denoted by a 'symbol'. Explain the meaning of the term 'symbol'. State a reason for representing the following elements by their symbols.

a) Hydrogen by $\mathrm{H}$

b) Helium by $\mathrm{He}$

c) Copper by $\mathrm{Cu}$

Match the metallic elements with their correct symbols.

Metallic elements - a) Potassium b) Sodium c)Calcium d) Magnesium e) Zinc f) Aluminium g)Iron h) Lead i) Copper j) Mercury k) Silver l) Platinum m) Gold

Symbols - $1. \mathrm{Ca} 2. \mathrm{Zn} 3. \mathrm{Pb} 4. \mathrm{Hg} 5. \mathrm{Cu} 6. \mathrm{Au} 7. \mathrm{K} 8. \mathrm{Fe} 9. \mathrm{Al} 10. \mathrm{Na} 11. \mathrm{Mg} 12. \mathrm{Pt} 13. \mathrm{Ag}$

Match the non-metallic elements with their correct symbols.

Non-metallic elements - a) Carbon b) Chlorine c) Oxygen d) Phosphorous e) Hydrogen f) Nitrogen g) Iodine h) Bromine i) Fluorine j) Silicon k) Sulphur

Symbols - $1. \mathrm{O} 2. \mathrm{I} 3. \mathrm{Si} 4. \mathrm{C} 5.\mathrm{Cl} 6. \mathrm{P} 7.\mathrm{F} 8. \mathrm{H} 9. \mathrm{S} 10. \mathrm{Br} 11. \mathrm{N}$

Match the noble gases with their correct symbols.

Noble gases - a) Helium b) Neon c) Argon d) Krypton e) Xenon f) Radon

Symbols - $1. \mathrm{Ar} 2. \mathrm{Xe} 3. \mathrm{Rn} 4. \mathrm{He} 5. \mathrm{Kr} 6. \mathrm{Ne}$