Which of the following allotropes of carbon is used as a lubricant? MCQ with Answer and Explanation

Explanation:
Concrete is a mixture of cement, fine aggregate (sand), coarse aggregate (gravel/crushed stone), and water. Mortar is cement + sand + water (no coarse aggregate). Plaster is cement/sand with water for coating walls. Asphalt is bitumen + aggregate. Concrete is strong in compression, used in buildings, bridges.

Explanation:
Boron trifluoride (BF₃) has covalent bonds where boron shares three electrons with three fluorine atoms. Although BF₃ can accept a lone pair to form coordinate bonds (as in BF₄⁻), its own bonds are polar covalent. Ionic bonding occurs between metal and non-metal.

Explanation:
Diamond is a giant covalent structure where each carbon is tetrahedrally bonded to four others via strong covalent bonds. Melting requires breaking numerous strong bonds, needing very high temperature (~3500°C). Graphite also has high melting point. Molecular solids like ice have low melting points. Carbon alone doesn't guarantee high m.p.; it's the structure.