In the reaction between acidified K₂Cr₂O₇ and iron (II) ions shown by the equation:

Cr₂${\mathrm{O}}_7^{2-}$(aq) + 6Fe²⁺(aq) +14H⁺(aq)$\to$2Cr³⁺(aq) + 7H₂O(l) + 6Fe³⁺(aq)

(a) the colour of the solution changes from green to blue

(b) the iron (II) ions are reduced 

(c) the dichromate ions are reduced 

(d) hydrogen ions are reduced

Which metal exhibits more than one oxidation states?

(1) Na

(2) Mg

(3) Al

(4) Fe

In which iron has the lowest oxidation state?

(a) Fe(CO)₅

(b) Fe₂O

(c) K₄Fe(CN)₆

(d) FeSO₄.(NH₄)₂SO₄.6H₂O

When an acidified solution of ferrous ammonium sulphate is treated with KMnO₄ solution, the ion which is oxidised is:

(a) Fe²⁺

(b) S${\mathrm{O}}_4^{2-}$

(c) N${\mathrm{H}}_4^{+}$

(d) Mn${\mathrm{O}}_4^{-}$

In the reaction,

2Na₂S₂O₃ + I₂ $\to$ Na₂S₄O₆ + 2NaI,

the oxidation state of sulphur is:

(1) decreased

(2) increased

(3) unchanged

(4) none of these

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

(1) Cr⁵⁺

(2) Cr⁴⁺

(3) Cr³⁺

(4) Cr²⁺

Which is not a redox change?

(a) CaCO₃ $\to$CaO + CO₂

(b) 2H₂ + O₂ $\to$2H₂O

(c) Na + H₂O $\to$ NaOH + 1/2 H₂

(d) MnCl₃ $\to$ MnCl₂ + 1/2 Cl₂

In the reaction;

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

which statement is correct?

(a) Br₂ is oxidised

(b) Br₂ is reduced

(c) Br₂ is neither oxidised nor reduced

(d) Br₂ is oxidised and reduced as well 

Which of the following colligative properties is associated with the concentration term 'molarity'?

(1) Lowering of vap.pressure

(2) Osmotic pressure

(3) Depression in freezing point

(4) Elevation in boiling point

Amongst the following identify the species with an atom in (+6) oxidation state.

1. Mn${\mathrm{O}}_4^{-}$

2. Cr$(\mathrm{CN}{)}_{}^{3-}6$

3. Ni${\mathrm{F}}_6^{2-}$

4. CrO₂Cl₂