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General ScienceEasyAsked in: NDA · NDA-II 2019, GAT

Which one of the following substances is not a mixture?

  1. A.Tin
  2. B.Sea water
  3. C.Soil
  4. D.Air

Correct answer

A. Tin

Explanation

The correct answer is A, Tin. Tin is a chemical element (symbol Sn, atomic number 50), a pure substance made of only one kind of atom, so it is not a mixture.

A pure substance has a fixed composition and fixed properties such as a definite melting point; elements and compounds are pure substances. A mixture contains two or more substances that are not chemically combined, keep their own properties and can be separated by physical methods such as evaporation, filtration or distillation. Tin is a soft, silvery metal used to coat steel cans and in alloys such as bronze (copper and tin) and solder.

B is wrong because sea water is a mixture of water with dissolved salts, mainly sodium chloride, which can be separated by evaporation.

C is wrong because soil is a mixture of rock particles, humus, water, air and living organisms.

D is wrong because air is a mixture of nitrogen (about 78%), oxygen (about 21%), argon, carbon dioxide and water vapour.

Exam tip: elements and compounds are pure substances; air, sea water, soil and alloys are mixtures.

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.