1. Convert milligrams to grams:

* 200 mg = 0.2 g (since 1 gram = 1000 milligrams)

2. Calculate the amount of NaCl:

* A 10% salt solution means that 10 grams of NaCl are present in every 100 grams of solution.

* Set up a proportion:

10 g NaCl / 100 g solution = x g NaCl / 0.2 g solution

* Solve for x:

x = (10 g NaCl * 0.2 g solution) / 100 g solution

x = 0.02 g NaCl

Therefore, there are 0.02 grams of NaCl in 200 mg of a 10% salt solution.