1
MCQ (Single Correct Answer)

AIPMT 2004

Which is the best description of the behaviour of bromine in the reaction given below?
H2O + Br2 $$ \to $$ HOBr + HBr
A
Proton acceptor only
B
Both oxidised and reduced
C
Oxidised only
D
Reduced only

Explanation

H2O + $${\mathop {Br}\limits^0}$$2 $$ \to $$ HO$$\mathop {Br}\limits^{ + 1} $$ + H$$\mathop {Br}\limits^{ - 1} $$

In the above reaction the oxidation number of Br2 increases from zero (in Br2 ) to +1 (in HOBr) and decreases from zero (in Br2 ) to –1 (in HBr). Thus Br2 is oxidised as well as reduced and hence it is a redox reaction.
2
MCQ (Single Correct Answer)

AIPMT 2003

The oxidation states of sulphur in the anions

SO3$${_3^{2 - }}$$, S2O$${_4^{2 - }}$$ and S2O$${_6^{2 - }}$$ follow the order
A
S2O$${_4^{2 - }}$$ < SO$${_3^{2 - }}$$ < S2O$${_6^{2 - }}$$
B
SO$${_3^{2 - }}$$ < S2O$${_4^{2 - }}$$ < S2O$${_6^{2 - }}$$
C
S2O$${_4^{2 - }}$$ < S2O$${_6^{2 - }}$$ < SO$${_3^{2 - }}$$
D
S2O$${_6^{2 - }}$$ < S2O$${_4^{2 - }}$$ < SO$${_3^{2 - }}$$

Explanation

SO32– : oxidation state of ‘S’ is +4

S2O42– : oxidation state of ‘S’ is +3.

S2O62– : oxidation state of ‘S’ is +5.

So, the order is S2O$${_4^{2 - }}$$ < SO$${_3^{2 - }}$$ < S2O$${_6^{2 - }}$$.

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