NEET 2018 Chemistry Questions with Answers and Explanation part 2 (11-20)

NEET 2018 Chemistry – Part 2 (Questions 11 to 20)

11. Which one is the correct order of acidity?
    (1) CH≡CH > CH₂=CH₂ > CH₃-CH₃
    (2) CH₃-CH₃ > CH≡CH > CH₂=CH₂
    (3) CH₂=CH₂ > CH≡CH > CH₃-CH₃
    (4) CH≡CH > CH₃-CH₃ > CH₂=CH₂
    Answer: (1)
    Explanation: Acidity order: Alkyne > Alkene > Alkane. Due to greater s-character in sp-hybridised C-H bond of alkyne.
12. The basic structure of metalloporphyrin, the prosthetic group in hemoglobin is:
    (1) Magnesium-porphyrin
    (2) Zinc-porphyrin
    (3) Iron-porphyrin
    (4) Cobalt-porphyrin
    Answer: (3)
    Explanation: Hemoglobin contains an iron-porphyrin complex called heme.
13. The difference between the standard enthalpies of formation of the reactants and products is called:
    (1) Enthalpy of reaction
    (2) Enthalpy of combustion
    (3) Bond dissociation energy
    (4) Lattice enthalpy
    Answer: (1)
    Explanation: ΔH_reaction = Σ ΔH_{f (products)} – Σ ΔH_{f (reactants)}
14. Which of the following ions exhibits color in aqueous solution?
    (1) Zn²⁺
    (2) Ti⁴⁺
    (3) Sc³⁺
    (4) V³⁺
    Answer: (4)
    Explanation: V³⁺ has d² configuration – unpaired electrons cause d–d transitions → color.
15. Which of the following is the strongest acid?
    (1) HClO
    (2) HClO₂
    (3) HClO₃
    (4) HClO₄
    Answer: (4)
    Explanation: Acid strength increases with more oxygen atoms. HClO₄ is the most oxidized and hence the strongest.
16. Which of the following statements is correct?
    (1) The gas constant R has the same units in all systems.
    (2) Gases deviate from ideal behavior at high temperature.
    (3) At low pressure, real gases behave like ideal gases.
    (4) The compressibility factor Z = PV/nRT = 0 for an ideal gas.
    Answer: (3)
    Explanation: At low pressure and high temperature, real gases approach ideal behavior.
17. Which of the following statements is incorrect?
    (1) All isotopes of a given element show the same chemical behavior.
    (2) Compounds of isotopes of a given element have different chemical behavior.
    (3) All isotopes of a given element have nearly the same atomic radii.
    (4) Isotopes of an element have different masses.
    Answer: (2)
    Explanation: Isotopes have same electronic configuration → similar chemical behavior.
18. Which one of the following ions has the highest spin-only magnetic moment value?
    (1) Fe³⁺ (d⁵)
    (2) Co²⁺ (d⁷)
    (3) Ni²⁺ (d⁸)
    (4) Cr³⁺ (d³)
    Answer: (1)
    Explanation: Fe³⁺ (d⁵) has 5 unpaired electrons → μ = √(n(n+2)) = √35 ≈ 5.92 BM.
19. Which of the following compounds contains a metal-carbon bond?
    (1) [Ni(CO)₄]
    (2) [Co(NH₃)₆]³⁺
    (3) [Fe(H₂O)₆]³⁺
    (4) [CrCl₆]³⁻
    Answer: (1)
    Explanation: [Ni(CO)₄] is a metal carbonyl complex with metal–carbon (Ni–C) bonds.
20. The order of reactivity of following alcohols with Lucas reagent is:
    (1) 1° < 2° < 3°
    (2) 3° < 2° < 1°
    (3) 2° < 3° < 1°
    (4) 1° < 3° < 2°
    Answer: (1)
    Explanation: Reactivity with Lucas reagent (ZnCl₂/HCl) increases with carbocation stability → 3° > 2° > 1°.