The correct answer is C. 200 mg.
One carat is equal to 200 milligrams (mg). It is a unit of mass used to measure gemstones, including diamonds. The carat is divided into 100 points, so a diamond that weighs 0.25 carats is also known as a quarter-carat diamond.
The carat is not a unit of weight in the traditional sense. It is a unit of mass, which is the amount of matter in an object. The weight of an object is the force of gravity acting on it. The mass of an object is the same everywhere, but its weight will vary depending on the strength of the gravitational field it is in.
The carat was originally defined as the weight of a seed from the carob tree. However, the weight of these seeds can vary, so the carat was later defined as 200 milligrams. This definition was adopted by the International Bureau of Weights and Measures in 1907.
The carat is the most common unit of mass used to measure gemstones. It is also used to measure pearls and other precious stones.