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Standard VII
Biology
Question

Four test tubes of tuhar dal were taken with some water in each and labelled as A, B, C and D. A few drops of the following were added to these test tubes.
Which of the test tube would be able to confirm the presence of metanil yellow adulterant ?
  1. Test tube C to which alcohol was added.
  2. Test tube D to which water was added.
  3. Test tube B to which HCl was added.
  4. Test tube A to which NaOH was added.

A
Test tube D to which water was added.
B
Test tube A to which NaOH was added.
C
Test tube B to which HCl was added.
D
Test tube C to which alcohol was added.
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Solution
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  • The dal is adulterated with a yellow coloured dye called metanil yellow.
  • The adulterant can be detected with the help of hydrochloric acid.
  • When a few drops of hydrochloric acid are added to the dal with metanil yellow, the colour of the solution turns pink.
  • This change in colour indicates that the dal is adulterated with metanil yellow.

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