Chemical Bonding and Molecular Structure Test 2

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Chemical Bonding and Molecular Structure Test 2

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Question 1
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Direction (Q. Nos. 1-15) This section contains 15 multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONLY ONE option is correct.
Q. By Lewis structure NO has following fact

A
Dot Lewis structure is

B
Bond order is 2.5 since, five electrons are shared between N and O-atom

C
There is one unpaired electron hence, NO is paramagnetic

D
All are correct facts

Solution

To complete octet, N shares 2 electrons and oxygen shares 3 electrons.

Thus, (a) is correct.
Question 2
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Lewis structure of HCI, H₂O and NH₃ are

A

B

C

D
None of the above is correct

Solution
Question 3
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The maximum covalency is equal to :

A
the number of unpaired p-electrons

B
the number of paired d-electrons

C
the number of unpaired s and p-electrons

D
total number of unpaired electron in ground state or in excited state

Solution

The maximum covalency is total no. of unpaired electron in ground state or in excited state which can be used for bond formation.
Question 4
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Which of the following has incomplete octet?

A
NH₃

B
BCI₃

C
CCI₄

D
PCI₃

Solution
Question 5
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Expansion of octet can not take place in

A
N

B
S

C
Si

D
P

Solution

N(7) = 1s²2s²2p³
Nitrogen does not have (2d) orbitals. Thus, (more than 8) electrons cannot be accommodated in the second orbit.
Question 6
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Which of the following is electron deficient?

A
(CH₃)₂

B
(SiH₃)₂

C
(BH₃)₂

D
PH₃

Solution
Question 7
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Based on valence bond theory, types of bonding in H₂O are

A
s-p

B
px^-px

C
Py^-P

D
Pz^-Pz

Solution
Question 8
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Bond order of (B— H) x and y bonds in diborane are respectively

A
1, 1

B
0, 0.5

C
0.5, 0.5

D
1, 0.5

Solution

Based on structure:

bond has one electron; bond order y = 0.5.
bond has two electrons; bond order x = 1.0.
Question 9
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Considering x-axis as the internuclear axis, which out of the following will not form sigma bond.

A
1s and 1s

B
1s and 2px

C
2py and 2py

D
1s and 2s

Solution
Question 10
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In which of the following molecules would you expect the N to N bond to be shortest ?

A
N₂H₄

B
N₂

C
N₂O₄

D
N₂O

Solution
Question 11
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Which of these molecules have non-bonding electron pairs on the central atom?
I. SF₄
II.ICI3
III. SO₂
IV. NH₃
V. SiF₄

A
All except V.

B
All except II and V.

C
All except I and V.

D
All except III and IV.
Solution
Nonbonding electron pairs means lonepair of electrons.
SF₄ molecule has one non-bonding electron pair on the central atom Sulfur.
ICl₃ molecule has two non-bonding electron pairs on the central atom Iodine.
SO₂ molecule has one non-bonding electron pair on the central atom Sulfur.
So the answer is D.
Question 12
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HCN and HNC molecules have equal number of

A
lone pairs and σ-bonds

B
o-bonds and π-bonds

C
π-bonds and lone pair

D
lone pairs, σ-bonds and π-bonds

Solution
Question 13
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When a chemical bond is formed, there is decrease in

A
kinetic energy

B
potential energy

C
repulsive force

D
attractive force

Solution

When two atoms approach to form a bond, there is decrease in potential energy (PE). After bond formation, at a minimum distance (called bond length). PE further increases.
Question 14
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Mean bond enthalpy of different bonds are given
Out of the given pairs, which compound is more stable than the other?

A

B

C

D

Solution

)bond enthalpy > )bond enthalpy hence, is stable.

Bond enthalpy of six (P— P) bond = 6 x 215 = 1290 k j mol^-1

Bond enthalpy of six (N — N) bond = 6 x 160
= 960 kJ mol^-1
Thus, P₄ is more stable than N₄.
Question 15
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Covalency of carbon in CO is three because

A
an unexcited carbon atom has two unpaired electrons

B
the C-atom can be an acceptor of an electron pair

C
the C-atom has four valence electrons

D
the maximum covalency of carbon is three

Solution

In structure I, octet of oxygen is complete but octet of carbon is incomplete. Hence, carbon is an acceptor of an electron pair from oxygen. Thus, covalency of carbon is three in CO.