1
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.
2
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.
3
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

When Cl2 gas reacts with hot and concentrated sodium hydroxide solution, the oxidation number of chlorine changes from
A
zero to +1 and zero to $$-$$5
B
zero to $$-$$1 and zero to +5
C
zero to $$-$$1 and zero to +3
D
zero to +1 and zero to $$-$$3

Explanation



This is an example of disproportionation reaction and oxidation state of chlorine changes from 0 to –1 and +5.
4
MCQ (Single Correct Answer)

AIPMT 2009

Oxidation numbers of P in PO$$_4^{3 - }$$, of S in SO$$_4^{2 - }$$ and that of Cr in Cr2O$$_7^{2 - }$$ are respectively
A
+3, +6 and +5
B
+5, +3 and +6
C
$$-$$3, +6 and + 6
D
+5, +6 and +6

Explanation

Let oxidation number of P in PO4 3– be x.

$$ \therefore $$ x + 4(–2) = –3

$$ \Rightarrow $$ x = +5

Let oxidation number of S in SO4 2– be y.

$$ \therefore $$ y + 4(–2) = –2

$$ \Rightarrow $$ y = +6

Let oxidation number of Cr in Cr2O7 2– be z.

$$ \Rightarrow $$ 2z + 7(–2) = –2

$$ \Rightarrow $$ z = +6

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