Neet 2019 Chemistry Question (16-30)

Q16. Which of the following is an electrophile?

A. NH₃
B. H₂O
C. AlCl₃
D. OH⁻

Answer: C

Explanation: AlCl₃ is electron deficient and accepts electron pairs – it's an electrophile.

Electrophiles are electron pair acceptors.

Q17. Which of the following contains both ionic and covalent bonds?

A. NaCl
B. NH₄Cl
C. CO₂
D. CaO

Answer: B

Explanation: NH₄⁺ has covalent bonds within the ion, and the Cl⁻ is ionically bonded.

Look for polyatomic ions like NH₄⁺ that have internal covalent bonds.

Q18. Which of the following statements is correct about enzymes?

A. They are inorganic catalysts
B. They are used up in reactions
C. They are specific biological catalysts
D. They are non-specific

Answer: C

Explanation: Enzymes are specific biological catalysts – usually proteins.

Enzymes act on specific substrates and speed up biological reactions.

Q19. Which of the following is not an isotope?

A. ¹H
B. ²H
C. ³H
D. ⁴He

Answer: D

Explanation: ¹H, ²H, ³H are isotopes (same atomic number), ⁴He is a different element.

Isotopes have same atomic number but different mass numbers.

Q20. Which of the following forms pπ–pπ multiple bonds?

A. HF
B. NH₃
C. O₂
D. CH₄

Answer: C

Explanation: O₂ forms a double bond through pπ–pπ overlap.

pπ–pπ bonding is found in molecules like O₂, N₂.

Q21. The bond angle in NH₃ is approximately:

A. 180°
B. 120°
C. 107°
D. 104.5°

Answer: C

Explanation: NH₃ has a trigonal pyramidal shape with ~107° bond angle.

Lone pair repulsion slightly reduces the ideal tetrahedral angle (109.5°).

Q22. Which of the following is not a greenhouse gas?

A. CO₂
B. CH₄
C. N₂
D. CFCs

Answer: C

Explanation: N₂ is not a greenhouse gas – it is non-polar and does not absorb IR.

Greenhouse gases absorb infrared radiation and contribute to global warming.

Q23. What is the IUPAC name of CH₃–CH(OH)–CH₃?

A. 1-Propanol
B. 2-Propanol
C. Propan-2-ol
D. Both B and C

Answer: D

Explanation: Both 2-Propanol and Propan-2-ol are correct IUPAC names.

Both naming styles are accepted; modern IUPAC prefers Propan-2-ol.

Q24. Which pair of elements belongs to the same period?

A. Na and Mg
B. Li and K
C. Be and Ba
D. Ca and K

Answer: A

Explanation: Na (Z=11) and Mg (Z=12) are in Period 3.

Periods are horizontal rows; groups are vertical columns.

Q25. In which of the following compounds does the central atom use sp² hybrid orbitals?

A. CH₄
B. NH₃
C. BF₃
D. H₂O

Answer: C

Explanation: In BF₃, B forms 3 sigma bonds → sp² hybridization.

sp² hybrid orbitals form trigonal planar geometry.

Q26. Which of the following does not show hydrogen bonding?

A. H₂O
B. NH₃
C. HCl
D. HF

Answer: C

Explanation: HCl does not form strong H-bonds due to less electronegative Cl.

H-bonding requires highly electronegative atoms like F, O, or N.

Q27. Which has the largest size?

A. Na⁺
B. Mg²⁺
C. Al³⁺
D. O²⁻

Answer: D

Explanation: O²⁻ has gained electrons → larger electron cloud, thus larger size.

Anions are larger than their neutral atoms; cations are smaller.

Q28. Which compound is used in breath analyzers to detect alcohol?

A. K₂Cr₂O₇
B. KMnO₄
C. I₂
D. AgNO₃

Answer: A

Explanation: K₂Cr₂O₇ oxidizes ethanol to acetic acid, changing color in the process.

The orange color of K₂Cr₂O₇ changes to green due to Cr³⁺ formation.

Q29. In which of the following compounds is the oxidation number of sulfur +6?

A. H₂S
B. SO₂
C. H₂SO₄
D. S₈

Answer: C

Explanation: In H₂SO₄, sulfur has +6 oxidation state.

Sum of oxidation numbers = overall charge; use known values to find unknown.

Q30. Which is used as a standard in NMR spectroscopy?

A. CCl₄
B. TMS
C. CHCl₃
D. CDCl₃

Answer: B

Explanation: TMS (Tetramethylsilane) is inert and gives a single sharp signal at 0 ppm.

TMS is used as internal reference in NMR due to its chemical stability and symmetry.