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All questions of Chemical Bonding and Molecular Structure for NEET Exam

Which of the following shows the Lewis dot formula for CO2?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

Gaurav Kumar answered
Step I: Skeleton OCO
Step II: A = 1 x 4 for C + 2 x 6 for O = 4 + 12 = 16 electrons
Step III : Total no. of electrons needed to achieve noble gas configuration (N)
N= 1 x 8 + 2 x 8 = 24
Step IV : Shared electrons, S = N- A = 24-16 = 8 electrons

Hybridisation of Acetylene is
  • a)
    sp
  • b)
    sp2
  • c)
    sp3
  • d)
    dsp2
Correct answer is option 'A'. Can you explain this answer?

Riya Banerjee answered
Since acetylene is made up of triple bond. So the hybridization of carbon in acetylene is sp.

Bond order of 1.5 is shown by : [2012]  
  • a)
    O2+
  • b)
    O2-
  • c)
    O22+
  • d)
    O2
Correct answer is option 'B'. Can you explain this answer?

Rajat Kapoor answered
N₂=N+N = 7e⁻+7e⁻ = 14e-  which has bond order =3 
O₂=8e⁻+8e⁻ = 16e⁻  which has bond order = 2
O₂⁺=8e⁻+8e⁻ - 1e⁻ = 15e⁻ which has bond order= 2.5
O₂⁻ = 8e⁻ +8e⁻ +1e⁻ =17 e⁻ which has bond order=1.5
So option B is correct .



Which of the following is nonpolar but contains polar bonds?
  • a)
    HCI
  • b)
    CO2
  • c)
    NH3
  • d)
    NO2
Correct answer is option 'A'. Can you explain this answer?

Pooja Mehta answered
This is why molecules like carbon dioxide are nonpolar despite having the polar carbon oxygen bonds. Molecules that contain non-polar bonds are not polar unless the central atom has one or more nonbonded pairs of electrons.

The correct order of increasing bond length of
I. C— H
II. C— O
III. C— C
  • a)
    I< II< III< IV
  • b)
    I< IV < II< III
  • c)
    Ill < IV < II < l
  • d)
    II < I < III < IV
Correct answer is 'B'. Can you explain this answer?

Amrita Sen answered
H is smallest in size thus, (C— H)bond length is least.


Hence, bonding pair in (C— O) is nearer to nucleus decreasing bond length as compared to (C— C).
Thus, I < IV < II < III.

Which of the following compounds has a 3-centre bond?[1996]
  • a)
    Diborane
  • b)
    Carbon dioxide
  • c)
    Boron trifluroide
  • d)
    Ammonia
Correct answer is option 'A'. Can you explain this answer?

Krish Saha answered
The bond represented by dots form the 3-centred electron pair bond. The idea of three centred electron pair bond B–H–B bridges is necessitated because diborane does not have sufficient electrons to  form normal covalent bonds. It has only 12 electrons instead of 14 required to give simple ethane like structure for diborane.

Valence Bond Theory was developed in the year
  • a)
    1916
  • b)
    1927
  • c)
    1930
  • d)
    1932
Correct answer is option 'B'. Can you explain this answer?

Krishna Iyer answered
The valence bond (VB) theory of bonding was mainly developed by Walter Heitler and Fritz London in 1927, and later modified by Linus Pauling to take bond direction into account. The VB approach concentrates on forming bonds in localized orbitals between pairs of atoms, and hence retains the simple idea of Lewis structures and electron pairs. 

Expansion of octet can not take place in
  • a)
    N
  • b)
    S
  • c)
    Si
  • d)
    P
Correct answer is option 'A'. Can you explain this answer?

Harshad Nair answered
N(7) = 1s22s22p3
Nitrogen does not have (2d) orbitals. Thus, (more than 8) electrons cannot be accomodated in second orbit.

The shape of the below molecule is
 
  • a)
    trigonal
  • b)
    rigonal planar
  • c)
    see saw
  • d)
    bent
Correct answer is option 'D'. Can you explain this answer?

Lavanya Menon answered
The order of Repulsion: lone pair-lone pair > lone pair-bond pair > bond pair-bond pair
Due to the extra lone pair electron, the shape becomes bent.

Which of the following angle corresponds to sp2 hybridisation?
a)120∘
b)180∘
c)90∘
d)109∘
Correct answer is option 'A'. Can you explain this answer?

sp2 hybridisation gives three sp2 hybrid orbitals which are planar triangular forming an angle of 120° with each other.
The electronic configurations of three elements A, B and C are given below.
Answer the questions from 14 to 17 on the basis of these configurations.
A ls22s22p6
B ls22s22p63s23p3
C ls22s22p63s23p

 Which molecule has a trigonal pyramidal shape?
  • a)
    AB4E
  • b)
    AB2E2
  • c)
    AB3E
  • d)
    AB2E
Correct answer is option 'C'. Can you explain this answer?

Geetika Shah answered
AB3E: trigonal pyramidal (central atom + 3 outer atoms make a pyramid)
→ start with AB4 molecule (tetrahedral) and replace a B atom w/ lone pair
→ lone pair electrons push bonding electrons away
→ bond angles are now less than 109.5°

In which of the following cases, covalent bonds are cleaved?
  • a)
    Boiling of H2O
  • b)
    Melting of KCN
  • c)
    Boiling of CF4
  • d)
    Melting of SiO2
Correct answer is option 'D'. Can you explain this answer?

Pooja Mehta answered
SiO2 is a network covalent compound that has an extremely high melting and boiling point, because many silicon-oxygen bonds have to be broken in order for it to achieve the necessary freedom. To clarify, SiO2, which has a tetrahedral network lattice formation, shows that each silicon is actually bonded to 4 oxygens; each oxygen is bonded to 2 silicon. These are excess bonds aside from the ones of SiO2 which are broken.

In which of the following ionizion processes, the bond order has increased and the magnetic behaviour has changed                                                                              [AIEEE-2007]
  • a)
    NO → NO+
  • b)
    O2 → 
  • c)
    N→ 
  • d)
    C2 → 
Correct answer is option 'A'. Can you explain this answer?

Raghav Bansal answered
N2: bond order 3, paramagnetic
N2-: bond order 2.5, paramagnetic
C2: bond order 2, diamagnetic
C2+: bond order 1.5, paramagnetic
NO: bond order 2.5, paramagnetic
NO+: bond order 3, paramagnetic
O2: bond order 2, paramagnetic
O2+: bond order 2.5, paramagnetic
Therefore, option a is correct

In BrF3 molecule, the lone pairs occupy equatorial positions to minimize [2004]
  • a)
    lone pair - bond pair repulsion only
  • b)
    bond pair - bond pair repulsion only
  • c)
    lone pair - lone pair repulsion and lone pair -bond pair repulsion
  • d)
    lone pair - lone pair repulsion only
Correct answer is option 'C'. Can you explain this answer?

In BrF3, both bond pairs as well as lone pairs of electrons are present. Due to the presence of lone pairs of electrons (lp) in the valence shell, the bond angle is contracted and the molecule takes the T-shape. This is due to greater repulsion between two lone pairs or between a lone pair and a bond pair than between the two bond pairs.

Which of the following species is paramagnetic ?
  • a)
    NO-
  • b)
    O22-
  • c)
    CN-
  • d)
    CO
Correct answer is option 'A'. Can you explain this answer?

Anjana Sharma answered
NO has an odd number of electrons and, therefore, must be paramagnetic. e. CO is diamagnetic because all of its electrons are paired.

Which is the correct order of the bond angle?
  • a)
    NH3 < NF3
  • b)
    H2O > Cl2O
  • c)
    PH< SbH3
  • d)
    H2Te < H2S
Correct answer is option 'D'. Can you explain this answer?

Nitin Patel answered

The high electronegativity of F pulls the bonding electrons farther away from N than in NH3. Thus, repulsion between bond pairs is iess in NF3 than in NH3. Flence, the lone pair in N causes a greater distortion than NH3.
(b) as in (a)

Going down the group in periodic table, as size of central atom increases, repulsion increases.

Select the correct statement(s) about IF7.
  • a)
    I atom is sp3d3-hybridised
  • b)
    I atom is in highest oxidation state
  • c)
    There are five I—F longest and two I—F shortest bonds
  • d)
    It has pentagonal bipyramidal structure
Correct answer is option 'A,B,C,D'. Can you explain this answer?

Rohit Shah answered
Iodine heptafluoride, also known as iodine(VII) fluoride or iodine fluoride, is an interhalogen compound with the chemical formula IF7.[2][3] It has an unusual pentagonal bipyramidal structure, as predicted by VSEPR theory.[4] The molecule can undergo a pseudorotational rearrangement called the Bartell mechanism, which is like the Berry mechanism but for a heptacoordinated system.[5] It forms colourless crystals, which melt at 4.5 degC: the liquid range is extremely narrow, with the boiling point at 4.77 degC. The dense vapor has a mouldy, acrid odour. The molecule has D5h symmetry. In IF7 out of 7 Flourine atoms 5 of them are placed on a plane in Pentagon shape .In remaining 2 flourines one is placed above the plane and other below the plane each at 90 degrees

Which of the following molecule doesn’t have a lone pair?
  • a)
    BeCl2
  • b)
    XeF4
  • c)
    NH3
  • d)
    H2O
Correct answer is option 'A'. Can you explain this answer?

Raghav Bansal answered
BeCl2 has no lone pairs on the beryllium. Thus, the electrons on the chlorides willtry to stay far apart from each other, since their corresponding electrons repel each other (while experiencing no deflection from electrons on a central atom). Thus themolecule is linear in shape.

Direction (Q. Nos. 13-16) This section contains 4 multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONE or  MORE THANT ONE  is correct.
Q.
In which of the following I is more volatile than II?
 
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A,B'. Can you explain this answer?

Hansa Sharma answered

I. Intermolecular H-bonding makes boiling point higher than that of I. Thus, I is more volatile 

II. Ortho nitrophenol is more volatile than para nitrophenol because O-Nitrophenol has intramolecular hydrogen bonding whereas para nitrophenol has inter molecular H bonding and so boils relatively at higher temperature
(c) BP of H2O > > H2S
(d) BP of CH3CH2OH (due to H-bonding) > > CH3— O — CH3 

Hydrogen bonds are formed in many compounds e.g., H2O, HF, NH3 . The boiling point of such compounds depends to a large extent on the strength of hydrogen bond and the number of hydrogen bonds. The correct decreasing order of the boiling points of above compounds is :
  • a)
    HF > H2O > NH3
  • b)
    H2O > HF > NH3
  • c)
    NH3 > HF > H2O ​
  • d)
    NH3 > H2O > HF
Correct answer is option 'B'. Can you explain this answer?

Neha Joshi answered
H2​O>HF>NH3​
Strength of hydrogen bonding depends on the size and electronegativity of the atom. 
Smaller the size of the atom, greater is the electronegativity and hence stronger is the H−bonding. Thus, the order of strength of H-bonding is H...F>H...O>H...N. 
But each HF molecule is linked only to two other HF molecules while each H2O molecule is linked to four other H2​O molecules through H−bonding.
Hence, the decreasing order of boiling points is H2​O>HF>NH3​.

Covalent nature of NaF, Na2O and Na3N in the increasing order is
  • a)
    Na3N < Na2O < NaF
  • b)
    NaF < Na2O < Na3N
  • c)
    Na2O < NaF < Na3N
  • d)
    Na2O < Na3 N < NaF
Correct answer is option 'B'. Can you explain this answer?

By Fajans' rule,
Smaller the size of cation, larger the size of anion. Larger the charge on cation or anion, larger the polarising power and thus, greater the covalent nature.
NaF, Na2O, Na3N, Na+ is same.

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