Skip to content
GK24
Prime
General ScienceHardAsked in: NDA · NDA-I 2025, GAT

Which one of the following nitrogen oxides may dimerize ?

  1. A.N2O
  2. B.NO2
  3. C.N2O3
  4. D.N2O5

Correct answer

B. NO2

Explanation

The correct answer is B, NO2. Nitrogen dioxide has an unpaired electron, so two of its molecules join to form dinitrogen tetroxide, N2O4.

A molecule of NO2 has an odd number of valence electrons (17), which makes it a free radical and gives it its reddish-brown colour. When two such molecules meet, the unpaired electrons pair up to form a bond between the two nitrogen atoms, giving colourless N2O4. The reaction 2NO2 ⇌ N2O4 is reversible: cooling favours the colourless dimer and heating brings back the brown gas, a standard experiment on chemical equilibrium.

A is wrong because N2O, laughing gas, has all its electrons paired and does not dimerise.

C is wrong because N2O3 is itself formed by joining NO and NO2; it does not dimerise further.

D is wrong because N2O5 is a stable molecule with paired electrons, the anhydride of nitric acid.

Exam tip: odd-electron molecules such as NO2 dimerise; brown NO2 turns into colourless N2O4 on cooling.

Practice Questions

View all
Q1.General ScienceAsked in: NDA · NDA-II 2018, GATMedium

If one set of chromosomes for a given plant is represented as N; in case of double fertilization, the zygote and the endosperm nucleus of a diploid plant would have how many sets of chromosomes respectively?

  1. A.N and 2N
  2. B.2N and 2N
  3. C.N and 3N
  4. D.2N and 3N
Show answer
Correct answer: D. 2N and 3N

The zygote is diploid (2N) and the primary endosperm nucleus is triploid (3N). Double fertilisation is a feature of flowering plants.

Q2.General ScienceAsked in: NDA · NDA-I 2019, GATEasy

Which one of the following statements is NOT correct for the given reaction? Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

  1. A.Iron is the reducing agent
  2. B.The solution turns green in colour after the reaction
  3. C.Copper is a more reactive metal than iron
  4. D.The reaction is an example of a redox reaction
Show answer
Correct answer: C. Copper is a more reactive metal than iron

The reaction happens because iron is more reactive than copper and pushes it out of its salt, so statement C is false.

Q3.General ScienceAsked in: NDA · NDA-II 2019, GATMedium

Which one of the following statements is correct ?

  1. A.Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres.
  2. B.Flexibility in plants is due sclerenchyma.
  3. C.Parenchyma have no intercellular spaces.
  4. D.Xylem consists of sieve plate, sieve tube and companion cells.
Show answer
Correct answer: A. Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres.

These four elements make up the complex tissue that carries water and minerals upward from the roots. Tracheids and vessels are long, dead, thick-walled tubes through which water moves; xylem parenchyma is the only living part and stores food; xylem fibres give support.

Q5.General ScienceAsked in: NDA · NDA-I 2022, GATHard

Which one of the following is not an example of a redox reaction?

  1. A.AlCl3 + 3H2O → Al(OH)3 + 3HCl
  2. B.2NaH → 2Na + H2
  3. C.4Fe + 3O2 → 2Fe2O3
  4. D.CuSO4 + Zn → Cu + ZnSO4
Show answer
Correct answer: A. AlCl3 + 3H2O → Al(OH)3 + 3HCl

This is a hydrolysis reaction in which no element changes its oxidation number, so nothing is oxidised or reduced. A redox reaction is one in which one substance loses electrons (its oxidation number rises) and another gains them (its oxidation number falls).