S - Block Elements MCQ Questions & Answers in Inorganic Chemistry | Chemistry
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111.
$$Be$$ and $$Al$$ exhibit diagonal relationship. Which of the following statements about them is/are not true?
(i) Both react with $$HCl$$ to liberate $${H_2}.$$
(ii) They are made passive by $$HN{O_3}.$$
(iii) Their carbides give acetylene on treatment with water.
(iv) Their oxides are amphoteric.
A
(iii) and (iv)
B
(i) and (iii)
C
(i) only
D
(iii) only
Answer :
(iii) only
The carbides of both $$Be$$ and $$Al$$ liberate methane with water.
$$\eqalign{
& B{e_2}C + 2{H_2}O \to 2BeO + C{H_4} \cr
& A{l_4}{C_3} + 6{H_2}O \to 2A{l_2}{O_3} + 2C{H_4} \cr} $$
112.
In all oxides, peroxides and superoxides, the oxidation state of alkali metals is
A
+ 1 and - 1
B
+ 1 and + 2
C
+ 1 only
D
+1, - 1 and + 2
Answer :
+ 1 only
All alkali metals have one valence electron and they readily lose this outermost electron to give $${M^ + }$$ ions.
113.
Which of the following has largest size ?
A
$$Na$$
B
$$N{a^ + }$$
C
$$N{a^ - }$$
D
$${\text{Can't be predicted}}$$
Answer :
$$N{a^ - }$$
$$N{a^ - }$$ has largest size because anion is always larger than neutral atom and cation is smaller than neutral atom. So the order is given as
$$\eqalign{
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,N{a^ - }\,\,\, > \,\,Na\,\, > \,\,N{a^ + } \cr
& {\text{Anion > Parental atom > Cation}} \cr} $$
114.
For which one of the following minerals, the composition given is incorrect?
A
Soda ash $$ - \left( {N{a_2}C{O_3}} \right)$$
B
Carnallite $$ - \left( {KCl.MgC{l_2}.6{H_2}O} \right)$$
C
Borax $$ - \left( {N{a_2}{B_4}{O_7}.7{H_2}O} \right)$$
D
Glauber's salt $$ - \left( {N{a_2}S{O_4}.10{H_2}O} \right)$$
115.
Which of the following statement about the sulphate of alkali metal is correct ?
A
Except $$L{i_2}S{O_4}$$ all sulphate of other alkali metals are soluble in water
B
All sulphate salts of alkali metals except lithium sulphate forms alum.
C
All sulphate salts of alkali metals except lithium sulphate do not decompose at high temperature
D
All of the above
Answer :
All of the above
All are facts
116.
The normal oxide contains _________ ion, peroxide contains _________ ion and superoxide contains _________ ion.
A
$${O^{2 - }},O_2^{2 - },O_2^ - $$
B
$${O^{2 - }},O_2^ - ,O_2^{2 - }$$
C
$${O^ - },{O^{2 - }},{O^{3 - }}$$
D
$${O^ - },{O^{2 - }},O_2^{2 - }$$
Answer :
$${O^{2 - }},O_2^{2 - },O_2^ - $$
No explanation is given for this question. Let's discuss the answer together.
117.
$$K{O_2}$$ (potassium super oxide) is used in oxygen cylinders in space and submarines because it
A
absorbs $$C{O_2}$$ and increases $${O_2}$$ content
B
eliminates moisture
C
absorbs $$C{O_2}$$
D
produces ozone.
Answer :
absorbs $$C{O_2}$$ and increases $${O_2}$$ content
$$2K{O_2} + 2{H_2}O \to 2KOH + {H_2}{O_2} + {O_2}.$$
$$K{O_2}$$ is used as an oxidising agent. It is used as air purifier in space capsules. Submarines and breathing masks as it produces oxygen and remove carbon dioxide.
118.
When plaster of Paris comes in contact with water it sets into a hard mass. The composition of the hard mass is
119.
$$A$$ metal $$M$$ readily forms its sulphate $$MS{O_4}$$ which is watersoluble. It forms its oxide $$MO$$ which becomes inert on heating. It forms an insoluble hyroxide $$M{\left( {OH} \right)_2}\,$$ which is soluble in $$NaOH$$ solution. Then $$M$$ is
A
$$Mg$$
B
$$Ba$$
C
$$Ca$$
D
$$Be$$
Answer :
$$Be$$
Sulphate of alkaline earth metal are sparingly soluble or almost not soluble in water whereas $$BeS{O_4}$$ is soluble in water due to high degree of solvation. $$Be{\left( {OH} \right)_2}$$ is insoluble in water but soluble in $$NaOH$$.
$$BeO + 2NaOH \to N{a_2}Be{O_2} + {H_2}O$$
120.
Solubility of the alkaline earth's metal sulphates in water decreases in the sequence
A
$$Mg > Ca > Sr > Ba$$
B
$$Ca > Sr > Ba > Mg$$
C
$$Sr > Ca > Mg > Ba$$
D
$$Ba > Mg > Sr > Ca$$
Answer :
$$Mg > Ca > Sr > Ba$$
Solubility of the sulphates. The sulphates becomes less soluble as you go down the group i.e. $$Mg > Ca > Sr > Ba$$
The magnitude of the lattice energy remains almost constant as the size of the sulphate ion is so big that small increase in the size of the cation from $$Be$$ to $$Ba$$ does not make any difference. However, the hydration energy decreases from $$B{e^{2 + }}$$ to $$B{a^{2 + }}$$ appreciably as the size of the cation increases down the group. The significantly high solubility of $$MgS{O_4}$$ is due to high enthalpy of solvation of the smaller $$M{g^{2 + }}\,ions.$$