In this question, we have a 0.1% solution, if we set up the percent concentration formula, which is:
C = w/v
We have to analyze the values given in the options and see which one would give us the value of 0.1% of solution, let's do it:
A. 0.001/100 = 0.00001, even in the percentage form (0.001%), this would not be the correct answer
B. 0.1/ml, this option does not give us a volume, so we can assume is 1 mL, therefore 0.1/1 = 0.1, in percentage, we have 10%
C. 0.1/100, this option will give us 0.001, but in the percentage form, we will have 0.1%, therefore this is the correct option
D. Very similar to letter B