Answer: Carbon (diamond, graphite, graphene, fullerene, amorphous carbon, nanotubes...).
- A Carbon (diamond, graphite, graphene, fullerene, amorphous carbon, nanotubes...)
- B Sulfur, which forms mainly the rhombic and monoclinic crystal forms in many documented cases
- C Phosphorus, which forms mainly the white and red allotropic forms according to conventional understanding
- D Oxygen, which forms mainly the dioxygen and ozone allotropic forms in routine practice
Correct answer: A. Carbon (diamond, graphite, graphene, fullerene, amorphous carbon, nanotubes...)
Explanation: Carbon has the most well-characterised allotropes: diamond, graphite, graphene, fullerenes (C<sub>60</sub>, C<sub>70</sub>...), carbon nanotubes, and amorphous forms.
Xenon tetrafluoride (XeF4) has six electron domains around xenon — four Xe–F bonds plus two lone pairs. The lone pairs occupy opposite axial positions, leaving the four fluorine atoms in a square-planar shape (Xe–F ≈ 194 pm). Image: ChemSim, Public Domain, via Wikimedia Commons.
Concept context
Covers the nitrogen family (Group 15), oxygen family (Group 16), halogens (Group 17), and noble gases (Group 18). One of the highest-weightage inorganic chapters in NEET and JEE - includes preparation and properties of HNO₃, H₂SO₄, interhalogens, and xenon compounds.