The correct answer is: $1000\ \mu\text{g}$
Explanation
A milligram (mg) is $10^{-3}$ grams and a microgram ($\mu$g) is $10^{-6}$ grams, so a milligram is 1000 times larger than a microgram.
Steps:
- $$1\ \text{mg}=10^{-3}\ \text{g}$$
- $$1\ \mu\text{g}=10^{-6}\ \text{g}$$
- $$\frac{1\ \text{mg}}{1\ \mu\text{g}}=\frac{10^{-3}}{10^{-6}}=10^{3}=1000$$
Therefore, $1\ \text{mg}=1000\ \mu\text{g}$.