In the reaction, 

Cr₂${\mathrm{O}}_7^{2-}$ +14H⁺ + 6I^- $\to$2Cr³⁺ + 7H₂O + 3I₂,

Which element is reduced?

1. I

2. O

3. H

4. Cr

2Na₂S₂O₃ + I₂ $\to$ Na₂S₄O₆ + 2NaI,

the oxidation state of sulphur in tha above reaction:

1. Decreases

2. Increases

3. Remain unchanged

4. None of the above

In the aluminothermic process, aluminium acts as:

1. an oxidising agent

2. a flux

3. a reducing agent

4. a solder

Disproportionation reaction(s) among the following is/are represented by -

1. Cl₂ + 2OH^- $\to$ClO^- + Cl^- + H₂O

2. Cu₂O(s) + 2H⁺ $\to$Cu²⁺ + Cu(s) + H₂O

3. 2HCuCl₂ $\underset{\mathrm{water}}{\overset{\mathrm{Dilution} \mathrm{with}}{\to }}$ Cu + Cu²⁺ + 4 Cl^- +  2H⁺

4. All of the above

During a redox change, the oxidant K₂Cr₂O₇ is always reduced to:

1. Cr⁵⁺

2. Cr⁴⁺

3. Cr³⁺

4. Cr²⁺

Oxidation state of +1 for phosphorus is found in:

1. H₃PO₃ 

2. H₃PO₄

3. H₃PO₂

4. H₄P₂O₇

Which of the following reactions does not represent a redox change?

1. CaCO₃ $\to$CaO + CO₂

2. 2H₂ + O₂ $\to$2H₂O

3. Na + H₂O $\to$ NaOH + \(\frac{1}{2}\)H₂

4. MnCl₃ $\to$ MnCl₂ + \(\frac{1}{2}\)Cl₂

If H₂S is passed through an acidified K₂Cr₂O₇ solution, the colour of the solution:

a. will remain unchanged

b. will change to deep red

c. will change to dark green

d. will change to dark brown 

The oxidation number and covalency of sulphur in the sulphur molecule (S₈) are respectively:

1. 0 and 2

2. +6 and 8

3. 0 and 8

4. +6 and 2

H₂S is passed through an acidified solution of copper sulphate and a black precipitate is formed. This is due to:

1. oxidation of Cu²⁺

2. reduction of Cu²⁺

3. double decomposition

4. reduction and oxidation