NEET-XII-Chemistry

Previous Year Paper year:2018

with Solutions - page 3
 
  • Qstn #75
    Which oxide of nitrogen is not a common pollutant
    introduced into the atmosphere both due to natural
    and human activity ?
    (1) ``\ce N2O5``
    (2) ``NO_2``
    (3) ``N_2O``
    (4) NO
    digAnsr:   1
    Ans : (1)
    Sol. Nitrous oxide (N2O) occurs naturally in environment.
    In automobile engine, when fossil is burnt dinitrogen
    & dioxygen combine to yield NO & NO2.
  • Qstn #76
    For the redox reaction
    ``\ce MnO4^-
    + C2O4^{2-}+ H^+
    \longrightarrow Mn^{2+} +CO2 + H2O``
    the correct coefficients of the reactants for the
    balanced equation are
    ``MnO_4^{-}`` ``C_2O_4^{2-}`` `` H^+``
    (1) 16 5 2
    (2) 2 5 16
    (3) 2 16 5
    (4) 5 16 2
    digAnsr:   2
    Ans : (2)
    Sol.
     7
    2
    4MnO Mn ; 5e gain
    +
     +  (1)
       + +
     
    3 4
    2
    2 4 2C O CO ; 2e loss (2)
    multiplying (1) by 2 and (2) by 5 to balance e-
      ++  +2 24 2 4 22MnO 5C O 2Mn 10CO
    on balancing charge;
      + ++ +  + +2 24 2 4 2 22MnO 5C O 16H 2Mn 10CO 8H O
    
    
    15
    CODE - PP
  • Qstn #77
    Which one of the following conditions will favour
    maximum formation of the product in the reaction,
    ``A_2(g) + B_2(g) \leftrightarrows X_2(g) \triangle_r``H = -X kJ ?
    (1) Low temperature and high pressure
    (2) Low temperature and low pressure
    (3) High temperature and high pressure
    (4) High temperature and low pressure
    digAnsr:   1
    Ans : (1)
    Sol. For reaction ▵H = - ve and ▵ng = - ve
    ∴ High P, Low T, favour product formation.
  • Qstn #78
    The correction factor 'a' to the ideal gas equation
    corresponds to
    (1) density of the gas molecules
    (2) volume of the gas molecules
    (3) electric field present between the gas molecules
    (4) forces of attraction between the gas molecules
    digAnsr:   4
    Ans : (4)
    Sol. Vanderwaal constant (a)  forces of attraction.
  • Qstn #79
    When initial concentration of the reactant is doubled,
    the half-life period of a zero order reaction
    (1) is halved (2) is doubled
    (3) is tripled (4) remains unchanged
    digAnsr:   2
    Ans : (2)
    Sol.  
     
    = 01 / 2 zero
    A
    t
    2K
    ∴ If [A]0 = doubled, t1/2 = doubled
  • Qstn #80
    The bond dissociation energies of ``X_2, Y_2 and XY``
    are in the ratio of 1 : 0.5 : 1.
    ``\triangle``H for the formation
    of XY is -200 kJ ``mol^{-1}``. The bond dissociation
    energy of ``X_2`` will be
    (1) 200 kJ ``mol^{-1}``
    (2) 100 kJ ``mol^{-1}``
    (3) 800 kJ ``mol^{-1}``
    (4) 400 kJ ``mol^{-1}``
    digAnsr:   3
    Ans : (3)
    Sol. let B.E. of x2 , y2 & xy are x kJ mol-1,
    0.5x kJ mol-1 and x kJ mol-1 respectively
    +  ▵ =  12 2
    1 1
    x y xy; H 200 kJmol
    2 2
    ▵H = - 200 = (B.E)Reactant - (B.E)Product
           =  +    
    1 1
    x 0.5x - 1 x
    2 2
    B.E of X2 = x = 800 kJ mol
    -1
  • Qstn #81
    Identify the major products P, Q and R in the
    following sequence of reaction :
    n81.png
    (1) n81a.png
    (2) n81b.png
    (3) n81c.png
    (4) n81d.png
    digAnsr:   4
    Ans : (4)
    Sol.
    Mech: CH -CH -CH -Cl3 2 2
    AlCl3 CH -CH -CH +AlCl3 2 2 4
    CH
    CH3 CH3
    (P)
    ESR
    CH -CH-CH3 3
    H
    shift
    -
    CH
    CH3 CH3
    Cumene

    C-O-O-HCH3
    CH3
    Cumene
    Hydroperoxide
    H O3
    +

    O2
    (P)
    OH
    Phenol
    + CH -C-CH3 3
    O
    Acetone
    (Q)
    (R)
    
    
  • Qstn #82
    Which of the following compounds can form a
    zwitterion ?
    (1) Aniline
    (2) Acetanilide
    (3) Benzoic acid
    (4) Glycine
    digAnsr:   4
    Ans : (4)
    Sol. The molecule which forms zwitter ion is glycine.
    HOOC-CH2 - NH2  O
    -
    OC-CH2 -

    N H3
    Zwitter ion
  • Qstn #83
    The type of isomerism shown by the complex
    [``CoCl_2(en)_2``] is
    (1) Geometrical isomerism
    (2) Coordination isomerism
    (3) Ionization isomerism
    (4) Linkage isomerism
    digAnsr:   1
    Ans : (1)
    Sol. Co
    Cl
    en en
    Cl
    Co en
    Cl
    Cl
    en
    Trans cis
  • Qstn #84
    Which one of the following ions exhibits d-d
    transition and paramagnetism as well ?
    (1) ``CrO^{2-}_4``
    (2) ``Cr_2O^{2-}_7``
    (3) ``MnO_4^{-}``
    (4) ``MnO_4^{2-}``
    digAnsr:   4
    Ans : (4)
    Sol. CrO4-2 Cr+6 diamagnetic
    Cr2O7
    -2 Cr+6 diamagnetic
    MnO4
    - Mn+7 diamagnetic
    MnO4
    -2 Mn+6 paramagnetic
    unpaired electron is present so d-d transition is
    possible.
    Before
    transition
    After
    transition
  • Qstn #85
    The geometry and magnetic behaviour of the
    complex [``Ni(CO)_4``] are
    (1) square planar geometry and diamagnetic
    (2) tetrahedral geometry and diamagnetic
    (3) square planar geometry and paramagnetic
    (4) tetrahedral geometry and paramagnetic
    digAnsr:   2
    Ans : (2)
    Sol. tetrahedral geometry and diamagnetic
    Ni 3d8 4s2
    CO is SFL so unpaired electrons will get paired.
    CO CO CO CO
    sp3 hybridisation
    Tetrahedral, diamagnetic
  • Qstn #86
    Iron carbonyl, ``Fe(CO)_5`` is
    (1) tetranuclear
    (2) mononuclear
    (3) trinuclear
    (4) dinuclear
    digAnsr:   2
    Ans : (2)
    Sol. Fe(CO)5
    EAN = Z-O.N. + 2(C.N.)
    = 26 - 0 + 2(5)
    = 26 + 10
    = 36
    only one central metal atom/ion is present and it
    follows EAN rule, so it is mononuclear
  • Qstn #87
    Match the metal ions given in Column I with the spin
    magnetic moments of the ions given in Column II
    and assign the correct code :
    Column I Column II
    a.`` Co^{3+}`` i. ``\sqrt8`` B.M.
    b. ``Cr^{3+}`` ii. ``\sqrt35`` B.M.
    c. ``Fe^{3+}`` iii. ``\sqrt3`` B.M.
    d. ``Ni^{2+}`` iv. ``\sqrt24`` B.M.
    v. ``\sqrt24`` B.M.
    a b c d
    (1) iv v ii i
    (2) i ii iii iv
    (3) iv i ii iii
    (4) iii v i ii
    digAnsr:   1
    Ans : (1)
    
    
    17
    CODE - PP
    Sol. Magnetic moment () =  +n n 2 B.M.
    (a) Co3+  1s2 2s2 2p6 3s2 3p6 4s0 3d6
    n = 4
      = + =4 4 2 24 B. M
    (b) Cr+3  1s2 2s2 2p6 3s2 3p6 4s0 3d3
    n = 3
      = + =3 3 2 15 B.M.
    (c) Fe3+  1s2 2s2 2p6 3s2 3p6 4s0 3d5
    n = 5
      = + =5 5 2 35 B. M.
    (d) Ni+2  1s2 2s2 2p6 3s2 3p6 4s0 3d8
    n = 2
      = + =2 2 2 8 B. M.
  • Qstn #88
    Which of the following is correct with respect to
    -I effect of the substituents ? (R = alkyl)
    (1)``\ce - NH2 < - OR < - F``
    (2) ``\ce -NR2 < - OR < - F``
    (3) ``\ce - NH2 > - OR > - F``
    (4) ``\ce - NR2 > - OR > - F``
    digAnsr:   1
    Ans : (1/2)
    Sol. (Based on EN)
    ∴ -NH2 < -OR < -F -I effect
    Also -NR2 < -OR < -F -I effect
  • Qstn #89
    Which of the following carbocations is expected to
    be most stable ?
    (1) n89a.png
    (2) n89b.png
    (3) n89c.png
    (4) n89d.png
    digAnsr:   3
    Ans : (3)
    Sol. -NO2 group is meta-directing group
    Y H Y H
    NO2NO2
    (Less stable due to more e- withdrawing effect of
    -NO2)
    H
    Y
    NO2NO2
    H
    Y
    NO2
    H
    Y
    (More stable due to less e- withdrawing effect of
    -NO2)