Final answer:
The measurement equal to one thousandth of a gram is known as a milligram. There are 1,000 milligrams in a single gram, and it's a unit commonly used in scientific contexts where very sensitive mass measurements are required.
Step-by-step explanation:
When we are discussing measurement, particularly how units of mass are related, it's important to understand that units can be converted into smaller or larger ones to accurately represent different weights or masses. Your question asks what measurement is equal to one thousandth of a gram. In the metric system, this is represented by the milligram (mg), which is indeed 1/1000th of a gram. Therefore, there are 1,000 milligrams in a single gram. This unit is much smaller than a gram and is commonly used in contexts that require a precise measurement of very light objects or substances, such as medicines or chemical compounds.
In our daily lives, we might not often use milligrams directly, since many objects we interact with are heavier. But in scientific contexts, particularly in laboratories where precision is crucial, milligrams are frequently used. Analytical balances in these laboratories are designed to measure mass very sensitively, often in grams or milligrams. Measurements in milligrams are so precise that they can measure something as light as a speck of dust.
To summarize and address the question's multiple choice options directly, 1 teaspoon is a volume measurement and is not equivalent to 1,000th of a gram in the mass, an ounce is an imperial unit of mass but is much heavier than a milligram, and the microgram is even smaller than a milligram and is not the correct choice either.
Therefore, the answer to your question is that the measurement equal to one thousandth of a gram is the milligram.