1
MCQ (Single Correct Answer)

AIPMT 2011 Prelims

Which of the following compounds has the lowest melting point?
A
CaCl2
B
CaBr2
C
CaI2
D
CaF2

Explanation

As the covalent character in compound increases and ionic character decreases, melting point of the compound decreases. So, CaI2 has the highest covalent character and lowest melting point.
2
MCQ (Single Correct Answer)

AIPMT 2011 Mains

Match List-I with List-II for the compositions of substances and select the correct answer using the code given above.

List-I
(Substances)
List-II
(Composition)
(A) Plaster of Pairs (i) CaSO4$$ \cdot $$2H2O
(B) Epsomite (ii) CaSO4$$ \cdot $$1/2 H2O
(C) Kieserite (iii) MgSO4$$ \cdot $$7H2O
(D) Gypsum (iv) MgSO4$$ \cdot $$H2O
(v) CaSO4
A
(A)-(iii),  (B)-(iv),  (C)-(i),  (D)-(ii)
B
(A)-(ii),  (B)-(iii),  (C)-(iv),  (D)-(i)
C
(A)-(i),  (B)-(ii),  (C)-(iii),  (D)-(iv)
D
(A)-(iv),  (B)-(iii),  (C)-(ii),  (D)-(i)

Explanation

(A) Plaster of paris = CaSO4.$${1 \over 2}$$H2O

(B) Epsomite = MgSO4.7H2O

(C) Kieserite = MgSO4.H2O

(D) Gypsum = CaSO4.2H2O
3
MCQ (Single Correct Answer)

AIPMT 2010 Prelims

Which one of the following compounds is a peroxide?
A
KO2
B
BaO2
C
MnO2
D
NO2

Explanation

4
MCQ (Single Correct Answer)

AIPMT 2010 Mains

The compound A on heating gives a colourless gas and a residue that is dissolved in water to obtain B. Excess of CO2 is bubbled through aqueous solution of B, C is formed which is recovered in the solid form. Solid C on gentle heating gives back A. The compound is
A
CaCO3
B
Na2CO3
C
K2CO3
D
CaSO4$$ \cdot $$2H2O

Explanation

A $$\buildrel \Delta \over \longrightarrow $$ colourless gas + residue

Residue + H2O $$ \to $$ B $$\buildrel {excess\,\,C{O_2}} \over \longrightarrow $$ C $$\buildrel \Delta \over \longrightarrow $$ A

This is possible only when ‘A’ is CaCO3. The reactions are as follow :

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