What is "Pure Gold" ? and what is meaning of " carat" with related to the purity of gold ?

Purity of ornamental gold is expressed in term of the "carat" and "24 carat gold" is 100%  pure on carat scale .

We know that 100%  gold is very soft so that not suitable for making ornaments then increases hardness of gond by adding silver or copper to make ornaments. Thus find the percentage of gold is "x" carat gold the % of gold and copper calculated as:

% of of gold in "20 carat gold" = 20/24×100= 83.33%