Can you convert a millogram into a milliliter?

Answer 1

No.

The first (assuming you meant milligram) is a measure of mass while the second is a measure of volume. For each substance, depending on its density, the conversion would be different.

Answer 2

No, milligrams and milliliters are units of different quantities (mass and volume, respectively) and cannot be directly converted to each other without additional information such as the density of the substance in question.