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Oxidation number of carbon in C₃O₂, Mg₂C₃ are respectively:

-4/3, +4/3

+4/3, -4/3

-2/3, +2/3

-2/3, +4/3

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Explanation

(b) Carbon has negative oxidation no. in Mg₂C₃ and positive oxidation number in C₃O₂, O is more electronegative than C. Mg is more electropositive than C.

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Which metal exhibits more than one oxidation states?

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Explanation

(d)

fe can show +2 and +3,as its a transition element

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The decomposition of KClO₃ to KCl and O₂ on heating is an example of:

intermolecular redox change

intramolecular redox change

disproportionation or auto redox change

none of the above

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Explanation

(b) 2KClO₃ $\to$ 2KCl + 3O₂. An intramolecular redox change is one in which one element of a compound is oxidised (O^2- to $O_{2}^{°}$ ) and one element is reduced (Cl⁵⁺ to Cl^1-).

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In which iron has the lowest oxidation state?

Fe(CO)₅

Fe₂O

K₄Fe(CN)₆

FeSO₄.(NH₄)₂SO₄.6H₂O

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Explanation

(a) Fe in Fe (CO)₅ has zero oxidation no., i.e., the lowest for metals.

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Which acts as a reducing agent?

HNO₃

KMnO₄

H₂SO₄

(COOH)₂

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Explanation

(d) Carbon in oxalic acid has +3 oxidation state which may be increased to +4 (in CO₂) and thus, can act as reductant. Rest all have highest oxidation number. Ox. no.of N, Mn and S in HNO₃(+5), KMnO₄(+7) and H₂SO₄(+6).

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The equivalent mass of a reductant or an oxidant is given by:

Eq. mass = $\frac{m o l a r m a s s o f r e d u c \tan t o r o x i d a n t}{n o . o f e l e c t r o n s l o s t o r g a i n e d b y 1 m o l e c u l e o f r e d u c \tan t o r o x i d a n t}$

Eq. mass = $\frac{m o l a r m a s s}{v a l e n c e}$

Eq. mass = $\frac{m o l a r m a s s}{t o t a l c h a r g e o n c a t i o n o r a n i o n}$

All of the above

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Explanation

(a) The formula for Eq. mass of reductant or oxidant.

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In the reaction,

NaH+ H₂O $\to$ NaOH + H₂:

H^- is oxidised

Na⁺is reduced

both NaH and H₂O are reduced

none of the above

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Explanation

(a) 2H^- $\to$ H₂+ 2e; Thus, H^- is oxidised.

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

Fe²⁺

S $O_{4}^{2 -}$

N $H_{4}^{+}$

Mn $O_{4}^{-}$

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Explanation

(a) Fe²⁺ $\to$ Fe³⁺ + e

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In the reaction,

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

Which element is reduced?

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Explanation

(d) C $r_{2}^{6 +}$ + 6e $\to$ 2Cr³⁺

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In the reaction,

2Na₂S₂O₃+ I₂ $\to$ Na₂S₄O₆ + 2NaI,

the oxidation state of sulphur is:

decreased

increased

unchanged

none of these

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Explanation

(b) 2 $S_{2}^{2 +}$ $\to$ $S_{4}^{5 / 2}$ +2e

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