The oxidation state of Ni in Ni(CO)₄ is:

(a) zero

(b) +4

(c) +8 

(d) +2

When SO₂ is passed through acidified solution of potassium dichromate, then chromium sulphate is formed. The change in oxidation number of chromium is:

(1) +4 to+2 

(2) +5 to+3

(3) +6 to+3

(4) +7 to+2

In the reaction;

2Ag + 2H₂SO₄ $\to$Ag₂SO₄ + 2H₂O + SO₂,H₂SO₄ acts as:

(1) oxidising agent

(2) reducing agent

(3) dehydrating agent

(4) none of these

In the equation,

N${\mathrm{O}}_2^{-}$ +  H₂O $\to$N${\mathrm{O}}_3^{-}$ + 2H⁺ + ne^-

n stands for:

(a) H⁺

(b) e^-

(c) 2e^-

(d) 3e^-

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⁺