Multiple choice

Water samples (X and Y) from two different sources were brought to the laboratory for the measurement of dissolved oxygen (DO) using modified Winkler method. Samples were transferred to 300 ml BOD bottles. 2 ml of MnSO4 solution and 2 ml of alkaliodide-azide reagent were added to the bottles and mixed. Sample X developed a brown precipitate, whereas sample Y developed a white precipitate.

In reference to these observations, the correct statement is

  1. Both the samples were devoid of DO.

  2. Sample X was devoid of DO while sample Y contained DO.

  3. Sample X contained DO while sample Y was devoid of DO.

  4. Both the samples contained DO.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In the Winkler method, a brown precipitate (manganese hydroxide) indicates the presence of dissolved oxygen, while a white precipitate indicates the absence of dissolved oxygen.

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