In 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

An element shows the most common oxidation state of −2.
What is the number of electrons present in its outermost shell?

1. 2

2. 4

3. 6

4. 8

4P + 3KOH + 3H₂O $\to$ 3KH₂PO₂ + PH₃:

Correct statement regarding the above reaction is:

1. P oxidised only

2. P is reduced only

3. P is oxidised as well as reduced

4. None of the above

In which SO₂ acts as oxidant, while reacting with:

1. acidified KMnO₄

2. acidified K₂Cr₂O₇

3. H₂S

4. H₂0₂

In the reaction;

3Br₂ + 6C${\mathrm{O}}_3^{2-}$ + 3H₂O $\to$5Br^- + Br${\mathrm{O}}_3^{-}$ + 6HC${\mathrm{O}}_3^{-}$

Which of the following statements is correct?

1. Br₂ is only oxidised.

2. Br₂ is only reduced

3. Br₂ is neither oxidised nor reduced

4. Br₂ is both oxidised and reduced.