1
MCQ (Single Correct Answer)

AIPMT 2015

On heating which of the following releases CO2 most easily?
A
Na2CO3
B
MgCO3
C
CaCO3
D
K2CO3

Explanation

Carbonates becomes more thermally stable down the group, Also, the alkali metal carbonate are more stable than alkaline earth metal carbonates. Therefore MgCO3 will leave CO2 easily.

MgCO3 $$\buildrel \Delta \over \longrightarrow $$ MgO + CO2
2
MCQ (Single Correct Answer)

NEET 2013 (Karnataka)

In Castner-Kellner cell for production of sodium hydroxide
A
brine is electrolyzed using graphite electrodes
B
molten sodium chloride is electrolysed
C
sodium amalgam is formed at mercury cathode
D
brine is electrolyzed with Pt electrodes

Explanation

In Castner-Kellner cell, sodium amalgam is formed at mercury cathode.
3
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

The ease of adsorption of the hydrated alkali metal ions on an ion-exchange resins follows the order :
A
Li+ < K+ < Na+ < Rb+
B
Rb+ < K+ < Na+ < Li+
C
K+ < Na+ < Rb+ < Li+
D
Na+ < Li+ < K+ < Rb+

Explanation

All alkali metal salts are ionic (except Lithium) and soluble in water due to the fact that cations get hydrated by water molecules. The degree of hydration depends upon the size of the cation. Smaller the size of a cation, greater is its hydration energy.

Relative ionic radii :

Li+ < K+ < Na+ < Rb+

Relative ionic radii in water or relative degree of hydration:

Rb+ < K+ < Na+ < Li+
4
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

Which one of the alkali metals, forms only, the normal oxide, M2O on heating in air?
A
Rb
B
K
C
Li
D
Na

Explanation

When alkali metals are heated in atmosphere of oxygen the alkali metals ignite and form oxides. On combustion, Li forms Li2O, sodium gives the peroxide Na2O2 while K and Rb give super oxides (MO2).

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