Clearly indicate your selection to answer the following questions. 2.1 Non-carbonate hardness comes from reaction of hardness ions with: a) carbonates nitrates b) bicarbonates c) carbon dioxide d) sulfates, chlorides, or 2.2 The titration agent used in hardness test is: a) silver nitrates b) sulfuric acid c) EDTA solution d) sodium hydroxides 2.3 A 25 mL of a sample are placed in a 300-mL BOD bottle with unseeded nutrient broth. The initial DO of the sample is 9.2 mg/L. The DO is 4.5 mg/L after 5 days. The 5-day BOD is around: a) 66 mg/L b) 96 mg/L c) 25 mg/L d) 56 mg/L 2.4 The standard guideline for hardness level according to World Health Organization WHO measured in mg/L as CaCO3: a) 250 b) 500 c) 750 d) 1000 2.5 If you can't run hardness test immediately, you need to preserve samples by adding 1.5 ml HNO3 per liter to bring pH to: a) <2 a) <4 a) <5 a) <8