Pure gold is very soft and therefore not suitable for making jewellery. To make it hard, gold is alloyed with other metals. The purity of gold is measured in carats according to the table below. Carat number is the number of parts of gold in 24 parts.

(a) What is the percentage of gold in 18 carat gold? Name any two metals that are used to make 22 carat gold.
(b) Like gold, pure iron is also comparatively soft and also undergoes rusting. Name the substance that is mixed with iron.
(i) to make it hard.
(ii) to change it to stainless steel to prevent rusting.