There are 1000mL per 1 L.

Mathematically.

1000mL

1L

If there are 1000mL in 1 L, then 1 mL is 1000th of a L.

Using dimensional analysis.

1 ~~mL~~ * 1 L = 0.001 L = 1 (10^{-3}) L = 1 mL

1000 ~~mL~~

So, 425.6789 mL =

425.6789 ~~mL ~~* 1 L =.4256789 L

1000 ~~mL~~

If there is 1 g in 1 mL, and 1000 mL in 1 L, then there are 1000g in a L, correct?

In this question you do not have 1g in 1 mL though.

Now, re-read all of DrCMS's posts.