The sequence of ionic mobility in aqueous solution is
A
Rb+ > K+ > Cs+ > Na+
B
Na+ > K+ > Rb+ > Cs+
C
K+ > Na+ > Rb+ > Cs+
D
Cs+ > Rb+ > K+ > Na+
Explanation
Smaller the size of an ion, greater will be
the degree of hydration. So, degree of hydration
is highest for Li+ and that is smallest for Cs+.
Therefore, Li+ holds the water molecules in its
hydration sphere and Cs+ ion holds the least water
molecules.
Hence, the correct ionic mobility in aqueous
medium is :
Cs+ > Rb+ > K+ > Na+
2
AIPMT 2008
MCQ (Single Correct Answer)
The alkali metals form salt-like hydrides by the direct synthesis at elevated temperature. The thermal stability of these hydrides decreases in which of the following orders?
A
NaH > LiH > KH > RbH > CsH
B
LiH > NaH > KH > RbH > CsH
C
CsH > RbH > KH > NaH > LiH
D
KH > NaH > LiH > CsH > RbH
Explanation
The stability of alkali metal hydrides
decreases from Li to Cs. It is due to the fact that M–H bonds becomes weaker with increase in
size of alkali metals as we move down the group
from Li to Cs. Thus the order of stability of
hydrides is
LiH > NaH > KH > RbH > CsH
3
AIPMT 2008
MCQ (Single Correct Answer)
Equimolar solutions of the following were prepared in water separately. Which one of the solutions will record the highest pH?
A
MgCl2
B
CaCl2
C
SrCl2
D
BaCl2
Explanation
Equimolar solutions of the given chlorides
when prepared in water forms their respective
hydroxides.
SrCl2 + 2H2O $$ \to $$ Sr(OH)2 + 2HCl
BaCl2 + 2H2O $$ \to $$ Ba(OH)2 + 2HCl
MgCl2 + 2H2O $$ \to $$ Mg(OH)2 + 2HCl
CaCl2 + 2H2O $$ \to $$ Ca(OH)2 + 2HCl
Be(OH)2
is amphoteric, but the hydroxides of other
alkaline earth metals are basic. The basic strength
increases down the group. Hence higher the basic
character higher will be the pH.
4
AIPMT 2007
MCQ (Single Correct Answer)
In which of the following the hydration energy is higher than the lattice energy?
A
MgSO4
B
RaSO4
C
SrSO4
D
BaSO4
Explanation
Hydration energy of sulphate decreases on
moving down the group-II. Mg2+ is smaller than
other ions of group II, so Mg2+ is readily hydrated
and hence MgSO4 has higher hydration energy
than the lattice energy.
Questions Asked from s-Block Elements
On those following papers in MCQ (Single Correct Answer)
Number in Brackets after Paper Indicates No. of Questions