Convert 400 mcg to mg.

To convert micrograms (mcg) to milligrams (mg), it is essential to know the relationship between the two units. Specifically, 1 milligram is equivalent to 1000 micrograms. Therefore, to convert from micrograms to milligrams, you can use the following formula:

[

\text{mg} = \frac{\text{mcg}}{1000}

]

Using this formula for the provided value:

[

\text{mg} = \frac{400 , \text{mcg}}{1000} = 0.4 , \text{mg}

]

This calculation shows that 400 micrograms is equal to 0.4 milligrams, which directly corresponds to the correct answer. Understanding this conversion is helpful not only for this particular question but also in practical nursing situations where precise medication dosing is critical.