Concept:Gold purity is measured in Karat (K). 24 Karat represents 100% pure gold.Explanation:Meter is a unit of length. Watt is a unit of power. Knot is a unit of speed for ships. None of these measure gold purity.Karat is the standard unit for expressing gold purity. It indicates the number of parts of pure gold present in 24 parts of the alloy.For example, 22 Karat gold means 22 parts are pure gold and 2 parts are other metals like copper or silver.Pure gold (24 Karat) is very soft and cannot be used for making jewellery, so alloys are created for strength.Higher Karat value means higher gold content in the item.Answer:Option B: Karat