S - Block Elements MCQ Questions & Answers in Inorganic Chemistry | Chemistry
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21.
Which of the following statements is not true about alkali metals?
A
All alkali metals form $$oxo$$ salts such as carbonates, sulphates and nitrates.
B
The basic character of oxides increases down the group.
C
Carbonates and sulphates of lithium are stable and their stability decreases down the group.
D
Solubility of carbonates and sulphates increases down the group.
Answer :
Carbonates and sulphates of lithium are stable and their stability decreases down the group.
Carbonates and sulphates of lithium decompose on heating while the stability of carbonates and sulphates of other metals increases down the group.
22.
Dead burnt plaster is
A
$$CaS{O_4}$$
B
$$CaS{O_4} \cdot \frac{1}{2}{H_2}O$$
C
$$CaS{O_4} \cdot {H_2}O$$
D
$$CaS{O_4} \cdot 2{H_2}O$$
Answer :
$$CaS{O_4}$$
No explanation is given for this question. Let's discuss the answer together.
23.
Compared with the alkaline earth metals, the alkali metals exhibit
A
smaller ionic radii
B
higher boiling points
C
greater hardness
D
lower ionisation energies
Answer :
lower ionisation energies
Alkali metals have the lowest ionisation enthalpy in each period because alkali metals are largest in their respective periods and therefore, the valency electrons are loosely held by the nucleus.
24.
Which of the following elements is extracted commercially by the electrolysis
of an aqueous solution of its compound ?
A
$$Cl$$
B
$$Br$$
C
$$Al$$
D
$$Na$$
Answer :
$$Na$$
Sodium is prepared by electrolysis of molten $$NaCl$$ as
\[\begin{align}
& 2NaCl\xrightarrow{\text{Electrolysis}}2Na+C{{l}_{2}} \\
& \text{At cathode:}\,\,2C{{l}^{-}}+2{{e}^{-}}\to C{{l}_{2}} \\
& \text{At anode:}\,\,\,\,\,\,2Na\to 2N{{a}^{+}}+2{{e}^{-}} \\
\end{align}\]
25.
Which of the following is known as fusion mixture ?
A
$${\text{Mixture of }}N{a_2}C{O_3} + NaHC{O_3}$$
B
$$N{a_2}C{O_3} \cdot 10{H_2}O$$
C
$${\text{Mixture of }}{K_2}C{O_3} + N{a_2}C{O_3}$$
D
$$NaHC{O_3}$$
Answer :
$${\text{Mixture of }}{K_2}C{O_3} + N{a_2}C{O_3}$$
A mixture of $$N{a_2}C{O_3}$$ and $${K_2}C{O_3}$$ is used as a fusion mixture.
26.
The first ionisation enthalpies of the alkaline earth metals are higher than that of alkali metals but second ionisation enthalpies are smaller, why?
A
In alkali metals, second ionisation enthalpy involves removal of electron from noble gas electronic configuration while in alkaline earth metals, second electron is removed from $$n{s^1}$$ configuration.
B
Alkaline earth metals have very high melting point as compared to alkali metals.
C
Electrons in $$s$$ - orbital are more closely packed in alkaline earth metals than alkali metals.
D
Due to smaller size alkaline earth metals do not form divalent ions very easily.
Answer :
In alkali metals, second ionisation enthalpy involves removal of electron from noble gas electronic configuration while in alkaline earth metals, second electron is removed from $$n{s^1}$$ configuration.
$${\text{Alkaline earth metals}} - $$
\[M-1{{e}^{-}}\xrightarrow{I{{E}_{1}}}\underset{n{{s}^{1}}}{\mathop{{{M}^{+}}}}\,\xrightarrow[-1{{e}^{-}}]{I{{E}_{2}}}\] \[\underset{\left( \text{Noble gas configuration} \right)}{\mathop{{{M}^{2+}}}}\,\]
$${\text{Alkali metals}}{\text{.}}$$
\[\underset{n{{s}^{1}}}{\mathop{M}}\,-1{{e}^{-}}\xrightarrow{I{{E}_{1}}}\underset{\left( \text{Noble gas configuration} \right)}{\mathop{{{M}^{+}}}}\,\] \[\xrightarrow[-1{{e}^{-}}]{I{{E}_{2}}}{{M}^{2+}};I{{E}_{2}}>>I{{E}_{1}}\]
27.
Arrange the following elements in the order of the increasing electropositive character.
$$Li,Na,K,Rb,Cs$$
A
$$Li > Na > K > Rb > Cs$$
B
$$Li < Na < K < Rb < Cs$$
C
$$Li > Na < K < Rb < Cs$$
D
$$Na > Li > K< Rb < Cs$$
Answer :
$$Li < Na < K < Rb < Cs$$
As ionisation energy decreases from $$Li$$ to $$Cs,$$ electropositive character increases from $$Li$$ to $$Cs.$$
28.
Lithium is the strongest reducing agent though it has highest ionisation energy in its group. Which of the following factors is responsible for making $$Li$$ the strongest reducing agent?
A
Large heat of atomisation
B
Smaller size
C
Large sublimation energy
D
Large amount of hydration enthalpy
Answer :
Large amount of hydration enthalpy
Large amount of hydration energy makes it strongest reducing agent inspite of its highest ionisation enthalpy.
\[{{M}_{\left( s \right)}}\xrightarrow[\text{energy}]{\text{Sublimation}}{{M}_{\left( g \right)}}\xrightarrow[\text{energy}]{\text{Ionisation}}\] \[M_{\left( g \right)}^{+}\xrightarrow[\text{energy}]{\text{Hydntion}}M_{\left( aq \right)}^{+}\]
29.
Aqueous solution of a group 2 element is precipitated by adding$$N{a_2}C{O_3},$$ then this precipitate is tested on flame, no light in visible region is observed , this element can be
A
$$Ba$$
B
$$Mg$$
C
$$Ca$$
D
$$Sr$$
Answer :
$$Mg$$
Electrons in $$Mg$$ due to its small size are tightly bound so they cannot be excited by the flame.
30.
Ionic mobility of which of the following alkali metal ions is lowest when aqueous solution of their salts are put under an electric field ?
A
$$Na$$
B
$$K$$
C
$$Rb$$
D
$$Li$$
Answer :
$$Li$$
Key concept More the extent of hydration, lesser is the ionic mobility.
In all the alkali metals, $$L{i^ + }\,ion$$ is smallest. Thus, extent of hydration is maximum in $$L{i^ + }\,ion.$$
i.e. the dissolution of $$L{i^ + }$$ in water occurs and get hydrated. Smaller the size of a cation, greater is the extent of hydration and lesser is the ionic mobility.