Chemical Bonding(12th Grade > Chemistry ) Questions and answers for exam Preparation

Question 1. The correct sequence of decrease in the bond angles of the following hydrides is

NH3> PH3> AsH3> SbH3
NH3> AsH3> PH3> SbH3
SbH3> AsH3> PH3> NH3
PH3> NH3> AsH3> SbH3

Explanation:-

Answer: Option A. -> NH3> PH3> AsH3> SbH3
:
A

N H_{3}

has

s p^{3}

hybridisation with bond angle

107^{0}

where as

P H_{3}, A s H_{3}, S b H_{3}

has pure orbitals overlapping with bond angle around

90^{0}

Question 2. Which of the following is false regarding dipole moments of the following

CH3Br> CH3I
BeCl2> SO2
NH3> NF3
HF >HCl

Explanation:-

Answer: Option B. -> BeCl2> SO2
:
B

B e C l_{2}

is linear with zero dipole moment &

S O_{2}

is angular with dipole moment

Question 3. The structure of

C H_{2} = C = C H_{2}

is

Linear
Planar
Non-planar
Has several resonance structures

Explanation:-

Answer: Option C. -> Non-planar
:
C
The pi bonds are at right angles to each other.

Question 4. Among the following which species has same number of

σ

and

π

bonds.

C7H8
C2(CN)4
C2H4
C2H2

Explanation:-

Answer: Option B. -> C2(CN)4
:
B
C₂(CN)₄ molecule contains 9

σ

and 9

π

bonds.

(C N)_{2} - C = C - (C N)_{2}

Each C bonded to N would have 2 pi and 1 sigma bond. So that is a total of 8 pi bonds. There is one pi bond between -C=C- in the middle.
The rest of the bonds are all sigma bonds - 1 each between C and N making a total of 4, 1 between the central carbon atoms, and 1 each between the central carbons and the C from CN, making a total of 9 sigma bonds.

Question 5. Which among the following compound have non-zero dipole moment?

Explanation:-

Answer: Option B. -> C2(CN)4
:
B

(μ \neq 0)

for the cis isomer:

Which Among The Following Compound Have Non-zero Dipole Mome...

The trans isomer has 0 dipole moment as expected:

Question 6. When the hybridization state of carbon atom changes from

s p^{3}

to

s p^{2}

and finally to

s p

, the angle between the hybridized orbitals:

Decreases gradually
Decreases considerably
Not effected
Increases progressively

Explanation:-

Answer: Option D. -> Increases progressively
:
D
From 109.28 to 120 to 180 degrees.

Question 7. Which of the following H-bonds is expected to have maximum strength?

H-O......H
H-N.......H
H-S.......H
All have same strength

Explanation:-

Answer: Option A. -> H-O......H
:
A
Oxygen is more electronegative than N, S

Question 8. H - B - H bond angle in

B H_{4}^{-}

is:

180o
120o
109o
90o

Explanation:-

Answer: Option C. -> 109o
:
C

B H_{4}^{-}

is tetrahedral

Question 9. The shape of covalent molecule

M X_{3}

is

Triangular
T - shaped
Pyramidal
Either of these depending on the number of lone pairs of electrons on M

Explanation:-

Answer: Option D. -> Either of these depending on the number of lone pairs of electrons on M
:
D
Shape depends on number of lone pair electrons

Question 10. The hybridisation of atomic orbitals of nitrogen in

{N O_{2}}^{+}

,

{N O_{3}}^{-}

and

{N H_{4}}^{+}

are:

sp, sp3 and sp2 respectively
sp, sp2 and sp3 respectively
sp2,sp and sp3 respectively
sp2,sp3 and sp respectively

Explanation:-

Answer: Option B. -> sp, sp2 and sp3 respectively
:
B