250+ TOP MCQs on Nucleophilic & Electrophilic Substitution Reaction and Answers

2. Which of the following statement is incorrect about nucleophiles?
a) Nucleophiles have an unshared electron pair and can make use of this to react with an electron deficient species
b) The nucleophilicity of an element (an electron donor) generally increases on going down a group in the periodic table
c) A nucleophile is electron-deficient species
d) All good nucleophiles are good bases when we deal across the period
Answer: c
Clarification: A nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond in relation to a reaction, it is an electron rich species.

3. What is the correct order of nucleophilicity in the following options?
a) (CH₃)₃CO^– > CH₃^–
b) CH₃S^– > CH₃SH
c) CH₃CH₂CH₂O^– < (CH₃)₃CO^–
d) (CH₃CH₂)₃N > (CH₃CH₂)₃P
Answer: b
Clarification: Alkoxides are weaker Nu^– than carbanion because negative charge on oxygen is more stable than carbon. CH₃CH₂CH₂O^– is more nucleophilic, due to less steric hindrance. The negative charge is more nucleophilic than a stable compound.

4. Which of the following order is correct for the solvolysis in 50% aqueous ethanol at 44.6^oC?
a)
b)
c)
d)
Answer: b
Clarification: Solvolysis is a nucleophilic substitution (S_N1) or elimination, where the nucleophile is a solvent molecule. Solvolysis order CH₃X < 1^o halide < 2^o halide < allylic halide < 3^o halide.

5. Identify correct step representing S_N1 mechanism for the cleavage of ether with HI.

a) 1 and 3
b) 2 and 3
c) 1 and 4
d) 2 and 4
Answer: b
Clarification: As we can see in below reaction first step is a slow step in which carbocation is formed. And the second step is fast where nucleophile will attach carbocation.