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D and F Block Elements question

2017 · Shift 2 · Q12
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D and F Block Elements question

2017 · Shift 2 · Q12

JEE AdvancedChemistryD and F Block ElementsMCQ+3 / −0.75
Which of the following combination will produce H2{H_2}H2​ gas ?
  1. A
    Fe metal and conc. HNO3HN{O_3}HNO3​
  2. B
    CuCuCu metal and conc. HNO3HN{O_3}HNO3​
  3. C
    ZnZnZn metal and NaOH(aq)NaOH(aq)NaOH(aq)
  4. D
    Au metal and NaCN(aq)NaCN\left( {aq} \right)NaCN(aq) in the presence of air
View written solutionFree

Correct answer: C

  1. We check each option for whether hydrogen gas, H2H_2H2​, is evolved.
  1. Option A: Fe metal and concentrated HNO3HNO_3HNO3​

Iron with concentrated nitric acid does not liberate H2H_2H2​.

  • Concentrated HNO3HNO_3HNO3​ is a strong oxidizing agent.
  • It oxidizes the metal and itself gets reduced to oxides of nitrogen such as NO2NO_2NO2​.
  • Also, iron becomes passive in concentrated HNO3HNO_3HNO3​ due to formation of an oxide layer.

So, H2H_2H2​ is not produced.

  1. Option B: Cu metal and concentrated HNO3HNO_3HNO3​

Copper reacts with concentrated nitric acid as:

Cu+4HNO3(conc.)→Cu(NO3)2+2NO2+2H2OCu + 4HNO_3(conc.) \rightarrow Cu(NO_3)_2 + 2NO_2 + 2H_2OCu+4HNO3​(conc.)→Cu(NO3​)2​+2NO2​+2H2​O

Here, the gas evolved is NO2NO_2NO2​, not H2H_2H2​.

So, Option B is incorrect.

  1. Option C: Zn metal and NaOH(aq)NaOH(aq)NaOH(aq)

Zinc is an amphoteric metal and reacts with aqueous sodium hydroxide to liberate hydrogen gas.

A common reaction is:

Zn+2NaOH+2H2O→Na2[Zn(OH)4]+H2↑Zn + 2NaOH + 2H_2O \rightarrow Na_2[Zn(OH)_4] + H_2 \uparrowZn+2NaOH+2H2​O→Na2​[Zn(OH)4​]+H2​↑

Thus, H2H_2H2​ gas is produced.

So, Option C is correct.

  1. Option D: Au metal and NaCN(aq)NaCN(aq)NaCN(aq) in presence of air

Gold dissolves in cyanide solution in the presence of oxygen/air by formation of a soluble cyanide complex:

4Au+8CN−+O2+2H2O→4[Au(CN)2]−+4OH−4Au + 8CN^- + O_2 + 2H_2O \rightarrow 4[Au(CN)_2]^- + 4OH^-4Au+8CN−+O2​+2H2​O→4[Au(CN)2​]−+4OH−

No hydrogen gas is evolved in this process.

So, Option D is incorrect.

  1. Final conclusion

Only zinc with aqueous sodium hydroxide produces hydrogen gas.

Therefore, the correct answer is:

C\boxed{C}C​
  1. Comparison with stored correct answer

Stored correct answer: C
Derived answer: C

They match.

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