BPSC PGT CHEMISTRY Important Questions- Organic Chemistry Basic Principles and Techniques

1. σ bonds are stronger than π bonds.
a) True
b) False

Answer: a
Explanation: In a σ bond, atoms overlap linearly, while in a π bond, the overlap is parallel. Since linear overlap is greater, the σ bond is stronger than the π bond.

2. How many σ and π bonds are present in the following molecule?
N≡C-CH-C≡N
a) σ = 5; π = 4
b) σ = 6; π = 3
c) σ = 4; π = 2
d) σ = 3; π = 5

Answer: a
Explanation: First, draw the complete Lewis structure of the molecule, ensuring that the valencies of all atoms are satisfied. Then, count the total number of bonds. In a triple bond, there is one sigma (σ) bond and two pi (π) bonds. In a double bond, there is one σ bond and one π bond. All single bonds consist of only σ bonds.

3. Arrange the following in the increasing order of electronegativity.
a) sp² < sp < sp³
b) sp³ < sp² < sp
c) sp < sp² < sp³
d) sp³ < sp < sp²

Answer: b
Explanation: The greater the s-character in hybrid orbitals, the higher the electronegativity. Among them, sp orbitals have 50% s-character, making them the most electronegative. In comparison, sp² orbitals have 33% s-character and sp³ orbitals only 25%, hence sp shows the highest electronegativity.

4. What is the hybridization of CH₃CH₂CH₂CN?
a) sp, sp³
b) sp², sp³
c) sp
d) sp, sp2

Answer: a
Explanation:

The structure of the compound is CH₃–CH₂–CH₂–C≡N. In this molecule, the carbon atoms forming only single bonds are sp³ hybridized, while the carbon involved in the triple bond with nitrogen is sp hybridized. Thus, CH₃CH₂CH₂CN contains both sp and sp³ hybridized carbons.

5. What is the valency of carbon?
a) Pentavalent
b) Divalent
c) Trivalent
d) Tetravalent

Answer: d
Explanation: Carbon has an atomic number of 6, giving it 4 valence electrons. In theory, it could gain or lose 4 electrons to achieve stability. However, losing 4 electrons is difficult because of the strong attraction between the nucleus and its electrons, and gaining 4 electrons is also unfavorable since the nucleus cannot effectively hold 8 extra electrons. Therefore, carbon attains stability by sharing electrons and forming four covalent bonds, which explains its tetravalency.