Answer:
1/20 g/mL
Step-by-step explanation:
You want the fraction form of the ratio in grams per mL of 50 g in 1000 mL.
The word "per" in this context means "divided by." That is, "grams per mL" means "grams divided by milliliters." That ratio looks like ...
[tex]\dfrac{50\text{ g}}{1000\text{ mL}}=\boxed{\dfrac{1}{20}\text{ g/mL}}[/tex]