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NCERT Exemplar · Class 10 Science Carbon and its Compounds

57 questions · 57 still being checked

Multiple Choice Questions 21–29 (part 3 of 6)

  1. Exercise 21

    Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g. hydrogen. After the formation of four bonds, carbon attains the electronic configuration of
    (a)
    helium
    (b)
    neon
    (c)
    argon
    (d)
    krypton

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    (b)
    (b) Neon. \[\mathrm{C}\ (2,4) \xrightarrow{\text{4 shared pairs}} \text{valence shell } 8e^- \equiv \mathrm{Ne}\ (2,8) \] Four bonding pairs fill carbon's outer shell to eight electrons -- the same outer-shell count as neon, the nearest noble gas.

  2. Exercise 22

    The correct electron dot structure of a water molecule is
    (a)
    H⋅O¨⋅⋅⋅H\displaystyle \mathrm{H} \cdot \underset{\cdot\cdot}{\ddot{\mathrm{O}}} \cdot \mathrm{H}
    (b)
    H:O¨⋅⋅⋅H\displaystyle \mathrm{H}: \underset{\cdot\cdot}{\ddot{\mathrm{O}}} \cdot \mathrm{H}
    (c)
    H:O¨⋅⋅:H\displaystyle \mathrm{H}: \underset{\cdot\cdot}{\ddot{\mathrm{O}}}: \mathrm{H}
    (d)
    H:O:H\displaystyle \mathrm{H}: \mathrm{O}: \mathrm{H}

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    (c)
    (c) \(\displaystyle \mathrm{H}:\underset{\cdot\cdot}{\ddot{\mathrm{O}}}:\mathrm{H}\) \[2\times 2\ (\text{lone pairs}) + 2\times 2\ (\text{shared pairs}) = 8\,e^- \text{ on O} \] (a) and (b) have a single-dot bond; (d) omits the lone pairs.

  3. Exercise 23

    Which of the following is not a straight chain hydrocarbon?
    (a)
    (b)
    H3C−CH2−CH2−CH2−CH2−CH3\displaystyle \mathrm{H}_3 \mathrm{C}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_3
    (c)
    (d)
    NCERT_Question_Class10_Science_Exemplar_Ch4_Q23
    NCERT_Question_Class10_Science_Exemplar_Ch4_Q23_2
    NCERT_Question_Class10_Science_Exemplar_Ch4_Q23_3

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    (d)
    (d) \(\displaystyle \mathrm{(H_3C)_2CH-CH_2-CH_2-CH_3}\) The \(\displaystyle \mathrm{CH}\) carbon bonds to three carbons, a branch; (a), (b), (c) are unbranched hexane.

  4. Exercise 24

    Which among the following are unsaturated hydrocarbons?
    (i)
    H3C−CH2−CH2−CH3\displaystyle \mathrm{H}_3 \mathrm{C}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_3
    (ii)
    H3C−C≡C−CH3\displaystyle \mathrm{H}_3 \mathrm{C}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_3
    (iii)
    (iv)
    (a) (i) and (iii)
    (b) (ii) and (iii)
    (c) (ii) and (iv)
    (d) (iii) and (iv)
    NCERT_Question_Class10_Science_Exemplar_Ch4_Q24
    NCERT_Question_Class10_Science_Exemplar_Ch4_Q24_2

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    (c)
    (c) (ii) and (iv). \(\displaystyle \mathrm{H_3C-C \equiv C-CH_3}\) carries a triple bond and \(\displaystyle \mathrm{H_3C-C(CH_3)=CH_2}\) a double bond -- both unsaturated; (i) \(\displaystyle \mathrm{H_3C-CH_2-CH_2-CH_3}\) and (iii) \(\displaystyle \mathrm{H_3C-CH(CH_3)-CH_3}\) hold only single bonds.

  5. Exercise 25

    Which of the following does not belong to the same homologous series?
    (a)
    CH4\displaystyle \mathrm{CH}_4
    (b)
    C2H6\displaystyle \mathrm{C}_2 \mathrm{H}_6
    (c)
    C3H8\displaystyle \mathrm{C}_3 \mathrm{H}_8
    (d)
    C4H8\displaystyle \mathrm{C}_4 \mathrm{H}_8

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    (d)
    (d) \(\displaystyle \mathrm{C_4H_8}\)\[\mathrm{CH_4,\ C_2H_6,\ C_3H_8}:\ \mathrm{C_nH_{2n+2}} \] \[\mathrm{C_4H_8}:\ \mathrm{C_nH_{2n}} \]Only \(\displaystyle \mathrm{C_4H_8}\) breaks the \(\displaystyle \mathrm{C_nH_{2n+2}}\) pattern shared by the other three.

  6. Exercise 26

    The name of the compound CH3−CH2−CHO\displaystyle \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CHO} is
    (a)
    Propanal
    (b)
    Propanone
    (c)
    Ethanol
    (d)
    Ethanal

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    (a)
    (a) Propanal\[\overset{3}{\mathrm{CH_3}}-\overset{2}{\mathrm{CH_2}}-\overset{1}{\mathrm{CHO}} \]Three carbons give the stem propan-; the terminal \(\displaystyle \mathrm{CHO}\) group gives the suffix -al.

  7. Exercise 27

    The heteroatoms present in
    CH3−CH2−O−CH2−CH2Cl\displaystyle \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{O}-\mathrm{CH}_2-\mathrm{CH}_2 \mathrm{Cl} are
    (i)
    oxygen
    (ii)
    carbon
    (iii)
    hydrogen
    (iv)
    chlorine
    (a) (i) and (ii)
    (b) (ii) and (iii)
    (c) (iii) and (iv)
    (d) (i) and (iv)

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    (d)
    (d) (i) and (iv)\[\mathrm{CH_3-CH_2-O-CH_2-CH_2Cl} \]A heteroatom is any atom other than C or H in the chain; here that is \(\displaystyle \mathrm{O}\) and \(\displaystyle \mathrm{Cl}\) — carbon and hydrogen form the backbone itself.

  8. Exercise 28

    Which of the following represents saponification reaction?
    (a)
    CH3COONa+NaOH→CaOCH4+Na2CO3\displaystyle \mathrm{CH}_3 \mathrm{COONa}+\mathrm{NaOH} \xrightarrow{\mathrm{CaO}} \mathrm{CH}_4+\mathrm{Na}_2 \mathrm{CO}_3
    (b)
    CH3COOH+C2H5OH→H2SO4CH3COOC2H5+H2O\displaystyle \mathrm{CH}_3 \mathrm{COOH}+\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \xrightarrow{\mathrm{H}_2 \mathrm{SO}_4} \mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5+\mathrm{H}_2 \mathrm{O}
    (c)
    2CH3COOH+2Na→2CH3COONa+H2\displaystyle 2 \mathrm{CH}_3 \mathrm{COOH}+2 \mathrm{Na} \rightarrow 2 \mathrm{CH}_3 \mathrm{COONa}+\mathrm{H}_2
    (d)
    CH3COOC2H5+NaOH→CH3COONa+C2H5OH\displaystyle \mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5+\mathrm{NaOH} \rightarrow \mathrm{CH}_3 \mathrm{COONa}+\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}

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    (d)
    (d)\[\mathrm{CH_3COOC_2H_5 + NaOH \rightarrow CH_3COONa + C_2H_5OH} \]Alkaline hydrolysis of an ester into the sodium salt of the acid and an alcohol is saponification; (a) is decarboxylation, (b) is esterification, (c) is a metal-acid reaction.

  9. Exercise 29

    The first member of alkyne homologous series is
    (a)
    ethyne
    (b)
    ethene
    (c)
    propyne
    (d)
    methane

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    (a)
    (a) Ethyne\[\mathrm{C_nH_{2n-2}},\quad n \geq 2 \] \[n=2:\ \mathrm{C_2H_2} = \text{ethyne} \]A \(\displaystyle \mathrm{C\equiv C}\) triple bond needs at least two carbons, so \(\displaystyle n=2\) is the smallest alkyne.