Which one of the following is not true for diamond?

Diamond is an allotrope of carbon where each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement [1]. This sp3 hybridization creates a rigid, three-dimensional network structure, making diamond the hardest naturally occurring substance [1]. Due to this extreme hardness, diamond is widely used as an abrasive for sharpening hard tools and for cutting or drilling applications. In contrast, graphite consists of hexagonal layers held by weak forces, allowing them to slide and act as a lubricant [1]. Diamond's rigid structure lacks this sliding capability and has no free electrons, making it unsuitable as a lubricant [1]. Therefore, the statement that diamond can be used as a lubricant is incorrect, as this property is characteristic of graphite's layered structure rather than diamond's rigid network [1].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Allotropes of carbon > p. 61