The number of structural isomers of pentane is

Pentane is an alkane with the molecular formula C5H12 [1]. Structural isomerism occurs when molecules share the same molecular formula but have different arrangements of atoms. For pentane, there are exactly three structural (constitutional) isomers. These include: 1) n-pentane, which is a straight-chain alkane; 2) isopentane (also known as 2-methylbutane), which features a branched four-carbon chain with a methyl group; and 3) neopentane (also known as 2,2-dimethylpropane), which has a central carbon atom bonded to four methyl groups [2]. While carbon can form millions of compounds due to its tetravalency and catenation properties, the specific arrangement of five carbon atoms in a saturated open chain is limited to these three distinct skeletal structures [1]. Therefore, the correct number of structural isomers for pentane is 3.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > QUESTIONS > p. 68
2. [2] https://en.wikipedia.org/wiki/Neopentane