Question

What is 24-carat gold? How will you convert it into 18-carat gold?

Answer 1

Hint: 24-carat gold is $99\cdot 9%$pure gold which has no other metal impurities added in it. It is bright yellow in appearance. 18-carat gold has copper or silver mixed along with gold. 24-carat gold can be converted to 18-carat gold by alloying it with copper or silver. This is done to increase its hardness.

Complete answer:
The word carat means parts per 24. 24-carat gold contains all 24 parts gold so it is the purest gold available. It is very soft because making jewelry with it becomes difficult as it is more prone to scratching and wear-tear. So it is converted to some other carat gold to increase its hardness so that it becomes efficient for making jewelry. 18-carat gold contains 18 parts per 24 i.e. $18/24=75\%$ gold and $25%$ alloy of silver or copper or we can say 18 parts pure gold and 6 parts alloy mixture.18-carat gold is harder than 24-carat gold due to which it is more suitable for jewelry. Addition of other metals makes the gold more durable. Since 24-carat gold is purer than 18-carat gold so it is more expensive.
One way to test gold’s purity is by holding it next to a magnet. Gold is not attracted by magnet so if 18-carat gold jewelry sticks to the magnet then it indicates that there are fewer parts per gold and other magnetic materials are added more which makes the gold impure.

Note:
Carat is a unit of purity for gold. Jewelry is expressed in ‘k’ or ‘kt’ and it is stamped in small numbers on the jewelry pieces. The addition of metals to 24-carat gold provides it more strength and durability and it is then available in 10k, 14k, 18k and 22k depending on the parts of gold and metals added to it. 18k gold is quite high in demand because it provides more durability and has a golden rich appearance. It is quite used for making wedding and engagement rings.