NEET 2018 Chemistry Questions – Part 3 (Q21–Q30)

NEET 2018 Chemistry Questions – Part 3 (Q21–Q30)

Welcome to Part 3 of our detailed NEET 2018 Chemistry question paper series. This section covers Questions 21 to 30 with correct answers and concise explanations. Perfect for NEET aspirants looking to understand key concepts and improve accuracy!

21. Which one of the following is the correct statement?
    (a) Chlorides of both beryllium and aluminium have bridged chloride structures in solid phase
    (b) B2H6·2NH3 is known as inorganic benzene
    (c) Boric acid is a protonic acid
    (d) Beryllium exhibits coordination number of six
    
    Answer: (a)
    Explanation: Both BeCl₂ and AlCl₃ show bridged chloride polymeric structures in the solid state.
22. The most suitable method of separation of 1:1 mixture of ortho and para-nitrophenols is:
    (a) Steam distillation
    (b) Crystallisation
    (c) Chromatography
    (d) Sublimation
    
    Answer: (a)
    Explanation: o-Nitrophenol forms intramolecular hydrogen bonds, making it steam volatile, unlike p-isomer.
23. Which oxide of nitrogen is not a common pollutant introduced into the atmosphere both due to natural and human activity?
    (a) N₂O
    (b) NO₂
    (c) N₂O₅
    (d) NO
    
    Answer: (c)
    Explanation: N₂O₅ is not a common atmospheric pollutant; others are released from combustion.
24. Which of the following compounds can form a zwitterion?
    (a) Aniline
    (b) Acetanilide
    (c) Benzoic acid
    (d) Glycine
    
    Answer: (d)
    Explanation: Glycine, an amino acid, has both –NH₂ and –COOH groups that can form a zwitterion.
25. The rate of a first-order reaction is 0.693 min^–1. Time taken for 75% completion of the reaction is:
    (a) 2 min
    (b) 1 min
    (c) 0.5 min
    (d) 0.25 min
    
    Answer: (a)
    Explanation: For 75% completion, t = 2t_1/2; t_1/2 = 0.693/k = 1 min → t = 2 min.
26. Which of the following is a natural polymer?
    (a) Polybutadiene
    (b) Polyethylene
    (c) DNA
    (d) PVC
    
    Answer: (c)
    Explanation: DNA is a naturally occurring biopolymer made of nucleotide monomers.
27. The species Ar, K⁺ and Ca²⁺ have the same number of electrons. Arrange them in increasing order of their radii:
    (a) Ar < K⁺ < Ca²⁺
    (b) Ca²⁺ < K⁺ < Ar
    (c) K⁺ < Ar < Ca²⁺
    (d) Ca²⁺ < Ar < K⁺
    
    Answer: (b) Ca²⁺ < K⁺ < Ar

21. Which of the following is not correct about carbon monoxide?
    (a) It forms carboxyhaemoglobin
    (b) It reduces oxygen carrying ability of blood
    (c) It combines with haemoglobin more efficiently than oxygen
    (d) It combines with oxygen to form CO₂
    
    Answer: (d)
    Explanation: CO does not directly combine with O₂ under normal conditions.
22. Which of the following ions exhibits d-d transition and paramagnetism as well?
    (a) Sc³⁺
    (b) Ti³⁺
    (c) Cu⁺
    (d) Zn²⁺
    
    Answer: (b)
    Explanation: Ti³⁺ has 1 d-electron, so it shows both paramagnetism and d-d transitions.
23. The IUPAC name of the compound CH₃CH=CHC≡CH is:
    (a) Pent-4-en-1-yne
    (b) Pent-1-en-4-yne
    (c) Pent-2-en-4-yne
    (d) Pent-2-en-1-yne
    
    Answer: (d)
    Explanation: The chain is numbered from the end closest to the double/triple bond. So, correct name is Pent-2-en-1-yne.

Tip for NEET aspirants: Understanding concept-based MCQs like these can help strengthen problem-solving strategies and boost scores.