Give reasons : Platinum, gold and silver are used to make jewellery.

A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?

$(i)$ Write the electron-dot structures for sodium. oxygen and magnesium.

$(ii)$ Show the formation of $Na _{2} O$ and $MgO$ by the transfer of electrons.

$(iii)$ What are the ions present in these compounds ?

You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Name two metals which are found in nature in the free state.