Give one example of an oxidation-reduction reaction which is also:(a) a combination reaction(b) a displacement reaction

(a) Combination reaction: 

 Carbon combines with oxygen to give carbon dioxide, heat energy is released during the process. Carbon is oxidised and oxygen is reduced.

$C\ ( s) \ +\ O_{2} \ ( g) \ \rightarrow \ CO_{2} \ +\ Heat$

$Carbon\ +\ Oxygen\ \rightarrow \ Carbon\ dioxide\ +\ Heat$

(b) Displacement reaction: 

 $CuO\ +\ H_{2}\xrightarrow{Heat} \ Cu\ +\ H_{2} O$

$Copper\ oxide\ +\ Hydrogen\xrightarrow{Heat} \ Copper\ +\ Water$

In the above reaction, copper oxide is reduced to copper and hydrogen is oxidixed to form water.