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SSC CGL 2022 PYQ — Question 29

SSC CGL - 19 April 2022 - Shift 3 • General Awareness • Q29

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Irrespective of the source, pure water contains ______ of oxygen by mass.

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Correct answer: B

Explanation

The correct answer is option 2 i.e. 88.89%.

  • The percentage of an element in a compound is 100 times the fraction, so for water the mass percent hydrogen is 11.11% and the mass percent oxygen is 88.89%.

  • One mole of water weights 18 grams, with 2 grams being hydrogen and 16 being oxygen, so the fraction of hydrogen is 2/18 (0.1111) and the fraction oxygen is 16/18 (.8889), and note that the sum of the fractions is 1.

  • The percentage of an element in a compound is 100 times the fraction, so for water the mass percent hydrogen is 11.11% and the mass percent oxygen is 88.89%.