Haloalkanes can be represented by the formula
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( C_nH_{2n+1}X \)
A haloalkane is formed when one hydrogen atom of an alkane is replaced by a halogen atom X. Alkanes have the general formula \( \ce{C_{n}H_{2n+2}} \). Removing one H and putting one X in its place gives:
\( \displaystyle \ce{C_{n}H_{2n+2}} \rightarrow \ce{C_{n}H_{2n+1}X} \)
So the general formula of a monohaloalkane is CnH2n+1X, that is, an alkyl group \( \ce{C_{n}H_{2n+1}-} \) joined to X (R–X). For example, n = 2 gives \( \ce{C2H5Cl} \), chloroethane.
Why the other options are incorrect
Option (1) \( C_nH_{2n+2}X \) — Incorrect. This keeps all the hydrogens of the alkane and adds X, which would need a carbon with five bonds.
Option (3) \( C_nH_{2n}X \) — Incorrect. This has one hydrogen fewer than the alkyl group; it is not a stable compound (with n = 2 it would be \( \ce{C2H4Cl} \)).
Option (4) \( C_nH_{n+2}X \) — Incorrect. The number of hydrogens does not match the four bonds of each carbon; for n = 2 it gives \( \ce{C2H4Cl} \), and for n = 4 it gives \( \ce{C4H6Cl} \), neither of which is a haloalkane.
NCERT (2026-27 edition):
Alkyl Halides or Haloalkanes (R—X) – “In alkyl halides, the halogen atom is bonded to an alkyl group (R). They form a homologous series represented by CnH2n+1X. They are further classified as primary, secondary or tertiary according to the nature of carbon to which halogen is attached.”