Final answer:
The unit of mass among the options is the gram (D). A gram is a small unit of mass, 1/1000th of a kilogram, which makes it suitable for laboratory work.
Step-by-step explanation:
The correct answer to the question “Which of the following is a unit of mass?” is D. gram. A gram is defined as exactly 1/1000 of the mass of a kilogram. The kilogram (kg) is the SI unit of mass, and one kilogram is equivalent to about 2.2 pounds. Other commonly used units of mass include the milligram (mg) and the pound. However, the pound is also considered a unit of weight whereas weight is affected by gravity and differs from mass which is a measure of the amount of matter. The gram is widely used in laboratory settings because it is a more practical measure for small-scale work.