
75. Given below are two statements:
Statement-I: Since fluorine is more electronegative
than nitrogen, the net dipole moment of NF3 is greater
than NH3.
Statement-II: In NH3, the orbital dipole due to
lone pair and the dipole moment of NH bonds are
in opposite direction, but in NF3 the orbital dipole
due to lone pair and dipole moments of N-F bonds
are in same direction.
In the light of the above statements. Choose the
most appropriate from the options given below.
(1) Statement I is true but Statement II is false.
(2) Both Statement I and Statement II are false.
(3) Both statement I and Statement II is are true.
(4) Statement I is false but Statement II is are true.
Ans. (2)
Sol.
76. The correct stability order of carbocations is
(1)
3 3 3 2 3 2 3
(CH ) C CH C H (CH ) C H C H
(2)
3 3 2 3 2 3 3
C H (CH ) C H CH C H (CH ) C
(3)
3 3 3 2 3 2 3
(CH ) C (CH ) C H CH C H C H
3 3 2 3 3
3
C H CH C H CH C H (CH )C
|
CH
Ans. (3)
Sol. More no. of hyperconjugable Hydrogens, more
stable is the carbocations.
77. The solution from the following with highest
depression in freezing point/lowest freezing point is
(1) 180 g of acetic acid dissolved in water
(2) 180 g of acetic acid dissolved in benzene
(3) 180 g of benzoic acid dissolved in benzene
(4) 180 g of glucose dissolved in water
Ans. (1)
Sol.
is maximum when i × m is maximum.
1)
, i = 1 +
Hence
ff
T (1 ) k 3 1.86 5.58 C ( 1)
2)
2 f f
180 3
m 3, i 0.5, T k ' 7.68 C
60 2
3)
3 f f
180 1.48
m 1.48, i 0.5, T k ' 3.8 C
122 2
4)
4 f f
180
m 1, i 1, T 1 k ' 1.86 C
180
As per NCERT,
1
f2
k ' (H O) 1.86 k kg mol
1
f
k ' (Benzene) 5.12 k kg mol
78. A and B formed in the following reactions are:
2 2 2
2 2 2
CrO Cl 4NaOH A 2NaCl 2H O
A 2HCl 2H O B 3H O
(1) A = Na2CrO4, B = CrO5
(2) A = Na2Cr2O4, B = CrO4
(3) A = Na2Cr2O7, B = CrO3
(4) A = Na2Cr2O7, B = CrO5
Ans. (1)
Sol.
2 2 2 4 2
(A)
CrO Cl 4NaOH Na CrO 2NaCl 2H O
2 4 2 2 5 2
Missing from
(B) balanced eqaution
Na CrO 2H O 2HCl CrO 2NaCl 3H O
79. Choose the correct statements about the hydrides
of group 15 elements.
A. The stability of the hydrides decreases in the
order NH3 > PH3 > AsH3 > SbH3 > BiH3
B. The reducing ability of the hydrides increases
in the order NH3 < PH3 < AsH3 < SbH3 < BiH3
C. Among the hydrides, NH3 is strong reducing
agent while BiH3 is mild reducing agent.
D. The basicity of the hydrides increases in the
order NH3 < PH3 < AsH3 < SbH3 < BiH3
Choose the most appropriate from the option given
below:
(1) B and C only (2) C and D only
(3) A and B only (4) A and D only
Ans. (3)
Sol. On moving down the group, bond strength of M–H
bond decreases, which reduces the thermal stability
but increases reducing nature of hydrides, hence A
and B are correct statements.