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 — A, 'if a substance loses hydrogen during reaction, it is reduced' is the statement that is NOT correct. In terms of hydrogen and oxygen, oxidation is gain of oxygen or LOSS of hydrogen, while reduction is loss of oxygen or gain of hydrogen. So losing hydrogen is oxidation, not reduction, which makes statement (a) the exception.
- (b)If a substance loses oxygen during reaction, it is reduced — This is correct. Loss of oxygen is the classic definition of reduction (for example CuO losing oxygen to become Cu), so it is a true statement and not the answer.
- (c)If a substance gains hydrogen during reaction, it is reduced — This is correct. Gain of hydrogen is reduction (for example ethene to ethane on hydrogenation), so the statement holds.
- (d)If a substance gains oxygen during reaction, it is oxidized — This is correct. Gain of oxygen is the textbook definition of oxidation (for example magnesium burning to MgO), so it is a true statement.
Using hydrogen and oxygen transfer, oxidation is the gain of oxygen or the loss of hydrogen, and reduction is the loss of oxygen or the gain of hydrogen. The two always happen together in a redox reaction: whatever one species gains, the other loses.
Three statements pair the change correctly; one flips it. Fix the four rules in mind — gain O or lose H is oxidation, lose O or gain H is reduction — and statement (a), which calls loss of hydrogen 'reduced', stands out as wrong. The wider mnemonic OIL RIG (Oxidation Is Loss, Reduction Is Gain of electrons) gives the same result.
- Oxidation is gain of oxygen or loss of hydrogen.
- Reduction is loss of oxygen or gain of hydrogen.
- Oxidation and reduction always occur together (a redox reaction).
- In electron terms, OIL RIG: Oxidation Is Loss, Reduction Is Gain of electrons.
Gain O or lose H = oxidation; lose O or gain H = reduction. Statement (a) reverses the hydrogen rule.
- Reversing the hydrogen rule (loss of H is oxidation, not reduction).
- Treating oxidation and reduction as separate, independent events.
- Confusing the substance oxidised with the oxidising agent.
NDA/UPSC list oxygen/hydrogen gain-loss statements and ask which is NOT correct — the reversed 'loss of hydrogen' rule is the planted error.
Consider the following statements: Coke is one of the materials of the charge added to blast furnace for the production of steel/iron. Its function is to I. Act as a reducing agent. II. Remove silica associated with the iron ore. III. Function as fuel, to supply heat. IV. Act as an oxidizing agent.
- (a) I and II are correct
- (b) II and IV are correct
- (c) I and III are correct
- (d) III and IV are correct
Answer(c) I and III are correct
Redox in an industrial setting. Coke reduces iron oxide to iron (reduction = loss of oxygen), the same reduction concept whose definitions this NDA statement question tests.
Which one among the following is an example of oxidation reaction?
- (a) Freezing of water
- (b) Dissolving sugar in water
- (c) Rusting of iron
- (d) Boiling of petrol
Answer(c) Rusting of iron
The same oxidation idea applied to a real change. Rusting is iron gaining oxygen (oxidation); this NDA-I question tests the very rule — gain of oxygen or loss of hydrogen is oxidation.
- practice — not a real PYQ
In the reaction CuO + H2 -> Cu + H2O, copper oxide is
- (a)oxidised
- (b)reduced
- (c)unchanged
- (d)neutralised
Answer(b) reduced — CuO loses oxygen to become Cu, which is reduction.
- practice — not a real PYQ
Loss of hydrogen by a substance during a reaction is an example of
- (a)reduction
- (b)oxidation
- (c)neutralisation
- (d)sublimation
Answer(b) oxidation — loss of hydrogen is oxidation, just as gain of oxygen is.