NEET Chemistry 3 — Questions and Answers
Question 1: Which of the following statements about SN1 reactions is correct?
- They proceed with inversion of configuration
- They follow first-order kinetics (Correct answer)
- They are favored by primary alkyl halides
- They involve a concerted mechanism
Correct answer: They follow first-order kinetics
SN1 reactions follow first-order kinetics because the rate-determining step is the unimolecular ionization of the substrate to form a carbocation.
Question 2: The molar conductivity of a weak electrolyte at infinite dilution can be determined using:
- Kohlrausch's law (Correct answer)
- Faraday's law
- Ostwald's dilution law
- Henry's law
Correct answer: Kohlrausch's law
Kohlrausch's law states that molar conductivity at infinite dilution equals the sum of individual ionic conductances, applicable to weak electrolytes.
Question 3: Which element shows the maximum tendency for catenation?
- Silicon
- Carbon (Correct answer)
- Germanium
- Tin
Correct answer: Carbon
Carbon shows maximum catenation due to its small size and strong C–C bond energy (~348 kJ/mol), forming stable long chains.
Question 4: The reaction of glucose with acetic anhydride gives:
- Glucose monoacetate
- Glucose pentaacetate (Correct answer)
- Glucose diacetate
- Glucose triacetate
Correct answer: Glucose pentaacetate
Glucose has five –OH groups, so it reacts with acetic anhydride to form glucose pentaacetate.
Question 5: Which of the following oxoacids of phosphorus is diprotic (dibasic)?
- H₃PO₄
- H₃PO₃ (Correct answer)
- H₃PO₂
- H₄P₂O₇
Correct answer: H₃PO₃
H₃PO₃ (phosphorous acid) is diprotic because one H is directly bonded to P (P–H bond), leaving only two ionizable –OH groups.
Question 6: For the reaction N₂ + 3H₂ ⇌ 2NH₃, if pressure is increased at constant temperature, the equilibrium will:
- Shift to the left
- Shift to the right (Correct answer)
- Remain unchanged
- First shift left then right
Correct answer: Shift to the right
Increasing pressure shifts equilibrium to the side with fewer moles of gas; 4 moles → 2 moles, so equilibrium shifts right (toward NH₃).
Question 7: The correct order of acidic strength among HF, HCl, HBr, HI is:
- HF > HCl > HBr > HI
- HI > HBr > HCl > HF (Correct answer)
- HCl > HBr > HI > HF
- HF > HI > HBr > HCl
Correct answer: HI > HBr > HCl > HF
Acid strength increases down the group as bond dissociation enthalpy decreases; HI is the strongest acid and HF the weakest.
NEET Chemistry 3
Which of the following statements about SN1 reactions is correct?