State what is observed when hydrochloric acid is added to silver nitrate solution.

Give the balanced equation:

When ethylene is burnt in an excess of oxygen.

Given balanced equation:

Ethylene reacts with chlorine.

Give balanced equation:

Ethylene combines with hydrogen chloride.

Give balanced equation:

A mixture of ethylene and hydrogen is passed over nickel at $150° \mathrm{C}$.

Give balanced equation:

Ethylene is heated at $400° \mathrm{C}$ under very high pressure in the presence of traces of ${\mathrm{O}}_2$.

What is the reaction taking place?

Give the function of acidified copper sulphate solution.