Why do gold and platinum not corrode in moist air? 

Which one is a chemical change- rusting of iron or melting of iron? 

What type of chemical reaction takes place when chlorine gas is passed through an aqueous solution of potassium bromide? 

Name the substance that has been oxidised in the reaction.

${\mathrm{H}}_2\mathrm{S}+{\mathrm{Cl}}_2\to 2\mathrm{HCl}+\mathrm{S}$

What is the significance of symbol 'aq'?