Which one of the following statements regarding oxidation and reduction reactions is NOT correct ?
- A.If a substance loses hydrogen during reaction, it is reduced
- B.If a substance loses oxygen during reaction, it is reduced
- C.If a substance gains hydrogen during reaction, it is reduced
- D.If a substance gains oxygen during reaction, it is oxidized
Correct answer
Explanation
The correct answer is A. A substance that loses hydrogen is oxidised, not reduced, so statement A is the incorrect one.
In the classical definitions, oxidation means the gain of oxygen or the loss of hydrogen, and reduction means the loss of oxygen or the gain of hydrogen. In terms of electrons, oxidation is the loss of electrons and reduction is the gain of electrons. For example, when hydrogen sulphide reacts with chlorine, H2S loses its hydrogen and is oxidised to sulphur. When copper oxide is heated with hydrogen, CuO loses oxygen and is reduced to copper, while hydrogen gains oxygen and is oxidised to water.
B is a correct statement, because losing oxygen is reduction.
C is a correct statement, because gaining hydrogen is reduction.
D is a correct statement, because gaining oxygen is oxidation.
Exam tip: oxidation = gain of oxygen, loss of hydrogen, loss of electrons; reduction is the opposite of each.
Practice Questions
View allIf 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?
- A.N and 2N
- B.2N and 2N
- C.N and 3N
- D.2N and 3N
Show answer
The zygote is diploid (2N) and the primary endosperm nucleus is triploid (3N). Double fertilisation is a feature of flowering plants.
Read the full explanation →Which one of the following statements is NOT correct for the given reaction? Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
- A.Iron is the reducing agent
- B.The solution turns green in colour after the reaction
- C.Copper is a more reactive metal than iron
- D.The reaction is an example of a redox reaction
Show answer
The reaction happens because iron is more reactive than copper and pushes it out of its salt, so statement C is false.
Read the full explanation →Which one of the following statements is correct ?
- A.Xylem consists of tracheids, vessels, xylem parenchyma and xylem fibres.
- B.Flexibility in plants is due sclerenchyma.
- C.Parenchyma have no intercellular spaces.
- D.Xylem consists of sieve plate, sieve tube and companion cells.
Show answer
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.
Read the full explanation →When light is scattered by a molecule and the frequency of the scattered light is changed, this phenomenon is called
- A.Rayleigh scattering.
- B.Raman effect.
- C.Photoelectric effect.
- D.Rutherford scattering.
Show answer
In the Raman effect, a small part of the light scattered by molecules comes out with a changed frequency. C.V.
Read the full explanation →Which one of the following is not an example of a redox reaction?
- A.AlCl3 + 3H2O → Al(OH)3 + 3HCl
- B.2NaH → 2Na + H2
- C.4Fe + 3O2 → 2Fe2O3
- D.CuSO4 + Zn → Cu + ZnSO4
Show answer
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).
Read the full explanation →