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Elements of Groups 16, 17 and 18 · Maharashtra Board STD 12 Science (MSBSHSE - English Medium). 23 questions.

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23 questions · self-marked practice — reveal the answer and mark yourself.

Question 11 Mark
Complete the following:
(1) $XeF _4+ H _2 O \rightarrow$ $\qquad$ $+ HF$
Answer
$XeF _4+ H _2 O \rightarrow XeOF _2+2 HF$
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Question 31 Mark
Explain the nature of zinc oxide with the help of the reactions.
###
Explain with chemical reactions, why is zinc oxide amphoteric in nature.
Answer
$ZnO _{( s )}+2 HCl _{( aq )} \longrightarrow ZnCl _{2( aq }+ H _2 O _{( a )}$
$ZnO _{( s )}+2 NaOH _{( aq )} \longrightarrow \underset{\text { Sodium zincate }}{ Na _2 ZnO _{2( aq )}+ H _2 O }$
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Question 41 Mark
Complete the following reactions :
(i) $H C l _{( g )}+ O _{2( g )} \xrightarrow[ CuCl _2]{\Delta}$
(ii) $S O _{2( g )}+ O _{2( g )} \xrightarrow{ V _2 O _5}$
Answer
(i) $4 HCl _{( g )}+ O _{2( g )} \xrightarrow[ CuCl _2]{\Delta} 2 H _2 O _{( g )}+2 Cl _{2( g )}$
(ii) $2 SO _{2( g )}+ O _{2( g )} \xrightarrow{ V _2 O _5} 2 SO _{3( g )}$
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Question 51 Mark
Write the reactions of dioxygen with
(i) $ZnS$
(ii) $CH _4$
Answer
(i) $2 ZnS _{( s )}+3 O _{2( g )} \xrightarrow{\Delta} 2 ZnO _{( s )}+2 SO _{2( g )}$ (ii) $CH _4+2 O _2 \xrightarrow{\Delta} CO _2+2 H _2 O$ Methane
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Question 71 Mark
Which are the most important allotropic forms of sulphur?
Answer
The most important allotropes of sulphur are :
  • Rhombic ($\alpha$-sulphur)
  • Monoclinic $(\beta$-sulphur)
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Question 91 Mark
Complete the following reactions :
(i) $Cu + S$
(ii) $Cd + Se$
Answer
(i) $Cu + S \rightarrow CuS$
(ii) $Cd + Se \rightarrow CdSe$

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Question 101 Mark
Complete the following reaction:
(i) $S+3 F_2$
(ii) $Se +2 Cl _2$
Answer
(i) $S +3 F _2 \rightarrow SF _6$
(ii) $Se +2 Cl _2 \rightarrow SeCl _4$
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Question 111 Mark
Complete the following reactions:
(i) $S + O _{2 \text { (air) }}$
(ii) $Se + O _{2 \text { (air) }}$
Answer
(i) $S + O _2 \xrightarrow{\Delta} SO _2$
(ii) $Se + O _2 \xrightarrow{\Delta} SeO _2$
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Question 121 Mark
Noble gases do not form compounds with hydrogen. Why?
Answer
Noble gases have a stable electronic configuration, and so are unreactive. Since, they are chemically inert, they do not form compounds with hydrogen.
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Question 131 Mark
Why does the tendency of group 16 elements to exist in -2 oxidation state decrease on moving down the group?
Answer
  • The electronegativity of the elements of Group 16 elements decreases on moving down the group in the order $O > S > Se > Te > Po$.
  • Thus, the tendency to show -2 oxidation state also decreases.
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Question 141 Mark
Why do sulphur and other heavier elements of group 16 exhibit higher oxidation states?
Answer
Since sulphur and heavier elements of group 16 have large atomic radii and available d-orbitals, they exhibit higher oxidation states.
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Question 151 Mark
Oxygen usually exhibits -2 oxidation state, but it exhibits +2 oxidation state in $OF _2$ ?
Answer
  • Oxygen being highly electronegative, it shows the common oxidation state – 2 in oxides.
  • In the presence of a highly electronegative fluorine atom it exhibits + 2 oxidation state in $OF _2$.
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Question 161 Mark
What is the oxidation state of oxygen in $OF _2$ ?
Answer
The oxidation state of oxygen in $OF _2$ is +2 .
$\begin{aligned}
& 1-2+1- \\
& ( F - O - F ) .
\end{aligned}$
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Question 171 Mark
What is the oxidation state of $S$ in $H _2 S _2 O _6$ ?
Answer
$\begin{array}{lll}
+2 & +10 & -12 \\
H _2 & S _2 & O _6
\end{array}$

$\therefore$ The oxidation state of $S$ atom $=+5$
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Question 181 Mark
Why does the density of halogens increase on moving down the group?
Answer
The bond dissociation enthalpies of halogen molecules decrease down the group with an increase in atomic size.
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Question 191 Mark
Why are halogens not found in the free state?
Answer
Halogens are highly reactive due to high elec-tronegativities, hence do not occur in the free state. They mostly occur in the form of compounds.
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Question 201 Mark
What are group 17 elements called?
Answer
Group 17 elements are collectively called halogens. In Greek, halo means salt and gene means born, so halogens are salt produClng elements.
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Question 211 Mark
What are chalcogens?
Answer
Group 16 elements are called chalcogens or ore-forming elements, as a large number of metal ores are oxides or sulphides.
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Question 221 Mark
What is the general electronic configuration of $p-$block elements?
Answer
The general electronic configuration of valence shell of $p-$block elements is $ns^2 np^{1 – 6} ($ except He which has electronic configuration $Is^2).$
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Question 231 Mark
To which groups in the periodic table do p-block elements belong?
Answer
A maximum of 6 electrons can be accommodated in the p-subshell, giving rise to six groups. In the periodic table, groups 13 to 18 include p-block elements.
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