The concentration of chloride ions in a water sample is estimated by titration with:

• A. Sodium thiosulphate reagent using ferrion as an indicator.
• B. Ferrous ammonium sulphate reagent using soluble starch as an indicator.
• C. Silver nitrate reagent using potassium chromate as an indicator.
• D. Silver nitrate reagent using potassium dichromate as an indicator.