NEET 2018 Chemistry Questions – Part 4 (Q31–Q40)

NEET 2018 Chemistry Questions – Part 4 (Q31–Q40)

31. The compound A on treatment with Na gives B, and with PCl₅ gives C. B and C react together to give diethyl ether. What is A?

    • (1) CH₃OH
    • (2) CH₃CH₂OH
    • (3) CH₃COOH
    • (4) C₂H₅COOH

    Answer: (2) CH₃CH₂OH

    Explanation: Ethanol reacts with Na to form sodium ethoxide (B) and with PCl₅ to form ethyl chloride (C). Ethyl chloride and sodium ethoxide react via Williamson’s synthesis to form diethyl ether.

32. The most suitable method for the separation of 1:1 mixture of ortho and para-nitrophenols is:

    • (1) Crystallisation
    • (2) Steam distillation
    • (3) Chromatography
    • (4) Sublimation

    Answer: (2) Steam distillation

    Explanation: o-Nitrophenol is steam volatile due to intramolecular H-bonding while p-nitrophenol is not. Hence, they can be separated by steam distillation.

33. Which oxide of nitrogen is not a common pollutant introduced into the atmosphere both due to natural and human activity?

    • (1) N₂O
    • (2) NO₂
    • (3) N₂O₅
    • (4) NO

    Answer: (3) N₂O₅

    Explanation: N₂O₅ is not commonly found as a pollutant; it is unstable and less commonly encountered in atmospheric chemistry.

34. Which of the following reactions is appropriate for converting acetamide to methanamine?

    • (1) Hoffmann hypobromamide reaction
    • (2) Stephens reaction
    • (3) Gabriels phthalimide synthesis
    • (4) Carbylamine reaction

    Answer: (1) Hoffmann hypobromamide reaction

    Explanation: Hoffmann degradation of acetamide yields a primary amine with one carbon less than the amide.

35. The major product of the following reaction is:
    CH₃CH=CHCH₂Br + KCN → ?

    • (1) CH₃CH=CHCH₂CN
    • (2) CH₃CH=CHCH(CN)₂
    • (3) CH₃CH=CHCOCH₃
    • (4) CH₃CH(CN)CH₂Br

    Answer: (1) CH₃CH=CHCH₂CN

    Explanation: KCN provides CN⁻ which replaces Br⁻ via SN2 mechanism.

36. The pair of species with identical shapes for molecules of both species is:

    • (1) SF₄ and XeF₄
    • (2) BF₃ and NH₃
    • (3) CF₄ and SiF₄
    • (4) XeF₂ and BrF₃

    Answer: (3) CF₄ and SiF₄

    Explanation: Both are tetrahedral molecules with sp³ hybridization.

37. Which of the following is not correct about carbon monoxide?

    • (1) It is a powerful reducing agent
    • (2) It forms carboxyhaemoglobin
    • (3) It reduces Fe₂O₃ in blast furnace
    • (4) The carboxyhaemoglobin is less stable than oxyhaemoglobin

    Answer: (4) The carboxyhaemoglobin is less stable than oxyhaemoglobin

    Explanation: Carboxyhaemoglobin is much more stable than oxyhaemoglobin, which is why CO poisoning is dangerous.

38. In the reaction: Zn + 2NaOH → Na₂ZnO₂ + H₂, zinc acts as:

    • (1) an oxidising agent
    • (2) a reducing agent
    • (3) an acid
    • (4) a base

    Answer: (2) a reducing agent

    Explanation: Zinc donates electrons and reduces water to hydrogen gas. So, it acts as a reducing agent.

39. Which of the following pairs does not require high temperature for thermal decomposition?

    • (1) CaCO₃ and NaNO₃
    • (2) Ba(NO₃)₂ and AgNO₃
    • (3) NaHCO₃ and NH₄NO₃
    • (4) MgCO₃ and Ca(NO₃)₂

    Answer: (3) NaHCO₃ and NH₄NO₃

    Explanation: Both decompose at relatively lower temperatures compared to others.

40. Which of the following reactions is used in the extraction of copper from low-grade ores?

    • (1) Electrolytic reduction
    • (2) Hydrometallurgy
    • (3) Zone refining
    • (4) Froth floatation

    Answer: (2) Hydrometallurgy

    Explanation: Hydrometallurgy involves dissolving ore in aqueous solution and then recovering the metal. It's suitable for low-grade ores like copper.