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General ScienceEasyAsked in: UPSC CAPF · CAPF 2017, Paper I

Which one of the following is the chemical name of heavy water?

  1. A.Hydrogen oxide
  2. B.Deuterium dioxide
  3. C.Deuterium oxide
  4. D.Heavy hydrogen oxide

Correct answer

C. Deuterium oxide

Explanation

The correct answer is C, Deuterium oxide. Heavy water is D₂O: two atoms of deuterium joined to one atom of oxygen.

Deuterium is the isotope of hydrogen with one proton and one neutron in its nucleus, so it is about twice as heavy as ordinary hydrogen. Water made with it has a molecular mass of about 20 instead of 18, is roughly 11 percent denser and freezes at about 3.8 degrees Celsius. Its main use is as a moderator in nuclear reactors, where it slows down fast neutrons without absorbing many of them, which lets reactors such as India's pressurised heavy water reactors run on natural uranium. Harold Urey discovered deuterium in 1931.

A is wrong because hydrogen oxide is ordinary water, H₂O. B is wrong because a dioxide would have two oxygen atoms, while heavy water has one. D is wrong because heavy hydrogen oxide is only an informal description, not the chemical name.

Exam tip: heavy water = D₂O, deuterium oxide, a moderator in PHWRs; deuterium discovered by Harold Urey.

Practice Questions

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Q1.General ScienceAsked in: UPSC Civil Services · CSE Prelims 2022, GS Paper IMedium

Which of the following are nitrogen-fixing plants?

1. Alfalfa

2. Amaranth

3. Chickpea

4. Clover

5. Purslane (Kulfa)

6. Spinach

Select the correct answer using the code given below:

  1. A.1, 3 and 4 only
  2. B.1, 3, 5 and 6 only
  3. C.2, 4, 5 and 6 only
  4. D.1, 2, 4, 5 and 6
Show answer
Correct answer: A. 1, 3 and 4 only

Alfalfa, chickpea and clover are legumes, and legumes fix nitrogen. Plants of the legume family (Fabaceae) carry root nodules that house Rhizobium bacteria.

Q2.General ScienceAsked in: UPSC CAPF · CAPF 2017, Paper IMedium

The mass number of an element is NOT changed when it emits

  1. A.Alpha and Beta radiations only
  2. B.Alpha and Gamma radiations only
  3. C.Beta and Gamma radiations only
  4. D.Alpha, Beta and Gamma radiations
Show answer
Correct answer: C. Beta and Gamma radiations only

Neither beta nor gamma emission changes the total number of protons and neutrons in a nucleus, so the mass number stays the same.

Q3.General ScienceAsked in: UPSC CAPF · CAPF 2025, Paper IMedium

Which one among the following statements about facilitated transport in plants is correct?

  1. A.All passive transports are types of facilitated transport.
  2. B.Facilitated transport is an example of active transport.
  3. C.Water moves across plasma membrane by active transport.
  4. D.Facilitated transport requires assistance of carrier proteins.
Show answer
Correct answer: D. Facilitated transport requires assistance of carrier proteins.

In facilitated transport, molecules cross the membrane with the help of membrane proteins, while still moving down their concentration gradient.

Q4.General ScienceAsked in: UPSC CAPF · CAPF 2017, Paper IMedium

Who among the following has coined the term 'Quark', the fundamental particles that make up protons and neutrons in an atomic nucleus ?

  1. A.Richard Feynman
  2. B.Murray Gell-Mann
  3. C.Albert Einstein
  4. D.Niels Bohr
Show answer
Correct answer: B. Murray Gell-Mann

The American physicist Murray Gell-Mann proposed quarks in 1964 and gave them their name. Gell-Mann, and independently George Zweig, suggested that protons, neutrons and other such particles are built from smaller units.