Comment on the oxidation states of the compounds copper $\left(\mathrm{I}\right)$ chloride,$\mathrm{CuCl}$ and copper $\left(\mathrm{II}\right)$ chloride, ${\mathrm{CuCl}}_2$.

Complete the given statement : 

Oxidation and reduction always ....

Magnesium reacts with sulphur dioxide like this : 

$2{\mathrm{Mg}}_{\left(\mathrm{s}\right)}+{\mathrm{SO}}_{2\left(\mathrm{g}\right)} \to 2{\mathrm{MgO}}_{\left(\mathrm{s}\right)}+{\mathrm{S}}_{\left(\mathrm{s}\right)}$

Show which substance is oxidised and which is reduced.

Explain where the term redox comes from.

Many people cook with natural gas, which is mainly methane, ${\mathrm{CH}}_4$. The equation for its combustion is : 

${\mathrm{CH}}_{4\left(\mathrm{g}\right)}+2{\mathrm{O}}_{2\left(\mathrm{g}\right)} \to {\mathrm{CO}}_{2\left(\mathrm{g}\right)}+2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}$

Show that this is a redox reaction.