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.

Carat number	Number of parts of gold in $24$ parts	Number of parts of other metals in $24$ parts
$24$	$24$	$0$
$22$	$22$	$2$
$18$	$18$	$6$
$14$	$14$	$1$
$12$	$12$	$12$

(a) What is the percentage of gold in $18$ carat gold? Name any two metals that are used to make $22$ carat gold.

b) (i) What type of mixture is an alloy?

(ii) How does the electrical conductivity of an alloy compare with that of the pure metal?