p-Block (18) — NEET UG Questions

7 NEET UG practice questions on p-Block (18), part of Chemistry. Below are 7 of them in full, each with the answer and a written explanation.

Questions & explanations

1. Which of the following statements is correct regarding the structure of xenon fluorides?

  1. XeF₂ has a bent (V-shaped) structure
  2. XeF₄ has a square planar structure
  3. XeF₆ has a perfect octahedral structure
  4. XeF₂ is prepared by heating a 1:5 mixture of Xe and F₂ at 300°C

Answer: XeF₄ has a square planar structure

XeF₄ has 4 bonding pairs and 2 lone pairs on the central Xe atom, giving it a square planar geometry. XeF₂ is linear, XeF₆ is distorted octahedral, and a 1:5 Xe:F₂ mixture yields XeF₄ at ~873 K (≈600°C, 7 bar), while XeF₂ forms from excess Xe at ~673 K and 1 bar — so option (d)’s “300°C” is incorrect.

2. Among the noble gases, which one forms stable compounds predominantly because of its relatively low ionization enthalpy and availability of d-orbitals for bonding?

  1. Helium
  2. Neon
  3. Argon
  4. Xenon

Answer: Xenon

Xenon has the lowest ionization enthalpy among the stable noble gases (excluding radioactive radon) and has accessible d-orbitals that allow it to expand its octet, enabling it to form stable compounds with highly electronegative elements like fluorine and oxygen.

3. Which of the following xenon compounds has a trigonal bipyramidal electron pair geometry around the central xenon atom?

  1. XeO₂F₂
  2. XeOF₄
  3. XeO₃
  4. XeF₄

Answer: XeO₂F₂

XeO₂F₂ has 5 electron pairs (2 double bonds, 2 single bonds, and 1 lone pair) around xenon, so its electron pair geometry is trigonal bipyramidal. The other compounds have different numbers of electron pairs leading to other geometries.

4. What is the primary reason for the extremely low chemical reactivity of noble gases?

  1. They exist as monoatomic gases at room temperature
  2. They have high atomic radii
  3. They have completely filled valence shells (ns²np⁶)
  4. They are present in very low concentrations in the atmosphere

Answer: They have completely filled valence shells (ns²np⁶)

The completely filled valence shell (octet) gives noble gases a highly stable electronic configuration, making them very reluctant to gain, lose, or share electrons, which accounts for their low reactivity.

5. The boiling points of noble gases increase down the group. Which one of the following correctly represents this trend?

  1. He > Ne > Ar > Kr > Xe
  2. He < Ne < Ar < Kr < Xe
  3. He > Ar > Ne > Xe > Kr
  4. He < Ne < Kr < Ar < Xe

Answer: He < Ne < Ar < Kr < Xe

Boiling points increase from He to Xe due to an increase in atomic size and the strength of London dispersion (van der Waals) forces, which depend on the number of electrons.

6. Which group of elements in the periodic table has the general valence shell electronic configuration ns²np⁶?

  1. Group 1
  2. Group 2
  3. Group 17
  4. Group 18

Answer: Group 18

The general valence shell configuration ns²np⁶ corresponds to a completely filled outermost shell, which is characteristic of noble gases belonging to Group 18.

7. Which noble gas is commonly used to fill balloons and airships because it is non-flammable and has very low density?

  1. Helium
  2. Neon
  3. Argon
  4. Krypton

Answer: Helium

Helium is lighter than air and chemically inert (non-flammable), making it ideal for filling balloons and airships, unlike hydrogen which is flammable.

More Chemistry topics

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