221.
Acidified solution of sodium thiosulphate is unstable because in thiosulphate A
the sulphur atoms are at unstable oxidation state of +2
B
the two sulphur atoms are at different oxidation states of +6 and -2
C
the $$S-S$$ bond are unstable bonds.
D
sulphur is in zero oxidation state.
Answer :
the two sulphur atoms are at different oxidation states of +6 and -2
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$$\mathop {N{a_2}{S_2}{O_3}}\limits_{{\text{(Disproportionation)}}} + 2HCl \to 2NaCl + S{O_2} + S + {H_2}O$$
222.
Metals form basic hydroxides. Which of the following metal hydroxide is the least basic? A
$$Mg{\left( {OH} \right)_2}$$
B
$$Ca{\left( {OH} \right)_2}$$
C
$$Sr{\left( {OH} \right)_2}$$
D
$$Ba{\left( {OH} \right)_2}$$
Answer :
$$Mg{\left( {OH} \right)_2}$$
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The basic character of metal hydroxides increases down the group from $$Mg{\left( {OH} \right)_2}$$ to $$Ba{\left( {OH} \right)_2}$$ due to increase in size, ionization enthalpy decreases and the $$M - O$$ bond becomes weaker.
223.
$$C{a^{2 + }}$$ is isoelectronic with A
$$Na$$
B
$$M{g^{2 + }}$$
C
$$B{a^{2 + }}$$
D
$$Ar$$
Answer :
$$Ar$$
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Both $$C{a^{2 + }}$$ and $$Ar$$ have 18 electrons.
224.
Which of the following does not show the anomalous behaviour of lithium? A
Lithium reacts with nitrogen to form a nitride.
B
Lithium carbonate decomposes on heating.
C
Lithium nitrate gives $$N{O_2}$$ on heating.
D
Lithium is the strongest reducing agent.
Answer :
Lithium is the strongest reducing agent.
225.
Which of the following is not correct about the solution when moderate amount of sodium metal is dissolved in liquid ammonia at low temperature? A
$$N{a^ + }\,ions$$ are produced in solution
B
We get a blue coloured solution
C
the solution acts as a good conductor of electricity
D
Liquid ammonia remains diamagnetic
Answer :
Liquid ammonia remains diamagnetic
226.
When sodium is dropped in small amount of water it catches fire. Which one of the following burns in the process? A
$$Na$$
B
$${H_2}O$$
C
$${H_2}$$
D
$$NaOH$$
Answer :
$${H_2}$$
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$${H_2}$$ gas produced during the reaction which burns in process.
227.
Which of the following statements is correct for $$CsB{r_3}?$$ A
It is a covalent compound.
B
It contains $$C{s^{3 + }}$$ and $$B{r^ - }\,ions.$$
C
It contains $$C{s^ + }$$ and $$Br_3^ - \,ions$$
D
It contains $$C{s^ + },$$ and $$B{r^ - }$$ and lattice $$B{r_2}$$ molecule.
Answer :
It contains $$C{s^ + }$$ and $$Br_3^ - \,ions$$
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$$CsB{r_3}$$ may be represented as $$C{s^ + }Br_3^ - $$
228.
Metallic magnesium is prepared by A
reduction of $$MgO$$ by coke.
B
electrolysis of aqueous solution of $$Mg{\left( {N{O_3}} \right)_2}.$$
C
displacement of $$Mg$$ by iron from $$MgS{O_4}$$ solution.
D
electrolysis of molten $$MgC{l_2}.$$
Answer :
electrolysis of molten $$MgC{l_2}.$$
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\[\begin{align}
& \underset{\text{(Molten)}}{\mathop{MgC{{l}_{2}}}}\,\xrightarrow{\text{Electrolysis}}\underset{\text{Cation}}{\mathop{M{{g}^{+2}}}}\,+\underset{\text{Anion}}{\mathop{2C{{l}^{-}}}}\, \\
& \text{Anode}\to 2C{{l}^{-}}\to 2Cl+2{{e}^{-}},Cl+Cl\to C{{l}_{2}} \\
& \text{Cathode}\to M{{g}^{+2}}+2{{e}^{-}}\to Mg \\
\end{align}\]
229.
Identify the correct statement. A
Gypsum is obtained by heating plaster of Paris
B
Plaster of Paris can be obtained by hydration of gypsum
C
Plaster of Paris is obtained by partial oxidation of gypsum
D
Gypsum contains a lower percentage of calcium than plaster of Paris
Answer :
Gypsum contains a lower percentage of calcium than plaster of Paris
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The formula of gypsum is $$CaS{O_4} \cdot 2{H_2}O$$ and that of plaster of Paris is $${\left( {CaS{O_4}} \right)_2} \cdot 2{H_2}O,$$ so the percentage of $$Ca$$ in plaster of Paris is more than gypsum.
230.
When sodium reacts with excess of oxygen, the oxidation number of oxygen changes from A
0 to - 1
B
0 to - 2
C
- 1 to - 2
D
no change
Answer :
0 to - 1
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$$2Na + \mathop {{O_2}}\limits^0 \to N{a_2}\mathop {{O_2}}\limits^{ - 1} $$