Question

given is the stock solution of 1000M.this solution is two fold serially diluted in 5 tubes. tell the concentration of solution in first tube , third tube and fifth tube​

Answer 1

Before entering into environmental analytical chemistry I would say to make a 1000 fold dilution, add 1000mL to 1 mL of what you're trying to dilute. But that's wrong, you add 999mL to 1mL of what you're trying to dilute. Reason is, it's already diluted once