This is a completely ambiguous question and I wish teachers and test-makers would stop writing questions like this. The answer depends entirely on the context of the problem. What do you intend to do with the solution, and what are you trying to measure?
If you are working with a procedure that requires you to weigh out your final material, a 1:10 dilution is designed to give you a 10% w/w (weight-to-weight) final solution. This means that when you weigh out 10 grams of your final solution, it will contain 1 gram of your starting component. In that case, you would use Twickels formulation - add 90 g water.
If you are working with a procedure that requires you to measure out your final solution by volume, a 1:10 dilution is designed to give you a 10% w/v (weight-to-volume) final solution. This means that when you measure out 10 mL of your final solution, it will contain 1 gram of your starting component. In that case, you would your proposed answer number 1 - put it in a volumetric flask and dilute it to 100 mL of total solution (fill to 100 mL mark). Since your question about reversing the calculations is using volumes, my guess is that this is actually the procedure you need to be using.
To do the calculations in reverse, you would just use the relationship that 10 mL of your test solution contained 1 gram of your initial solution.
ChemBuddy | 
Chem Reddit | 
Topic: Dilution Calculation (Read 14369 times)