1
MCQ (Single Correct Answer)

AIPMT 2014

In acidic medium, H2O2 changes Cr2O72- to CrO5 which has two

($$-$$O$$-$$O$$-$$) bonds. Oxidation state of Cr in CrO5 is
A
+5
B
+3
C
+6
D
$$-$$10

Explanation

CrO5 has butterfly structure having two peroxo bonds.



Peroxo oxygen has –1 oxidation state.

Let oxidation state of Cr be ‘x’

CrO5 : x + 4(–1) + 1 (–2) = 0

$$ \Rightarrow $$ x = +6
2
MCQ (Single Correct Answer)

AIPMT 2014

(I)   H2O2 + O3 $$ \to $$ H2O + 2O2
(II)   H2O2 + Ag2O $$ \to $$ 2Ag + H2O + O2
Role of Hydrogen peroxide in the above reactions is respectvely
A
oxidizing in (I) and reducing in (II)
B
reducing in (I) and oxidizing (II)
C
reducing in (I) and (II)
D
oxidizing in (I) and (II)

Explanation



So, H2O2 acts as reducing agent in all those reactions in which O2 is evolved.
3
MCQ (Single Correct Answer)

AIPMT 2014

The pair of compounds that can exist together is
A
FeCl3, SnCl2
B
HgCl2, SnCl2
C
FeCl2, SnCl2
D
FeCl3, KI

Explanation

Both FeCl2 and SnCl2 are reducing agents with low oxidation numbers.
4
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

A mixture of potassium chlorate, oxalic acid and sulphuric acid is heated. During the reaction which element undergoes maximum change in the oxidation number?
A
S
B
H
C
Cl
D
C

Explanation

KClO3 + C2H2O4 + H2SO4 $$ \to $$ K2SO4 + CO2 + KCl + H2O

Maximum change in oxidation number of chlorine, i.e., from +5 to –1.

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