The hardest natural substance is: MCQ with Answer and Explanation

Explanation:
Allotropes are different structural forms of the same element. Diamond has a tetrahedral sp³ network, while graphite has a planar sp² layered structure. This difference in atomic arrangement results in distinct physical properties: diamond is hard, transparent, insulating; graphite is soft, black, conducting. Allotropes have same chemical composition (pure carbon). Other allotropes include fullerenes and graphene.

Explanation:
Soda-lime glass is produced by fusing silica (SiO₂) with sodium carbonate (Na₂CO₃) and calcium carbonate (CaCO₃) at high temperature. Na₂CO₃ acts as flux to lower melting point, CaCO₃ provides stability. Reaction: Na₂CO₃ + SiO₂ → Na₂SiO₃ + CO₂. Sodium chloride is not used. Potassium compounds make harder glass.

Explanation:
In BF₃, boron has 3 valence electrons and forms 3 covalent bonds with fluorine, resulting in only 6 electrons in its valence shell. It does not complete its octet, making it an electron-deficient molecule and a strong Lewis acid. NH₃, H₂O, and CH₄ all have complete octets.