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Which halogen halide is least reactive?
(A) HI
(B) HCl
(C) HBr
(D) HF

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Last updated date: 20th Jul 2024
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Answer
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Hint :Alkyl halides (also known as haloalkanes) are alkanes that have had one or more hydrogen atoms substituted by halogen atoms (fluorine, chlorine, bromine or iodine). Haloalkanes are a class of chemical compounds made up of alkanes that contain one or more halogens. While the distinction is not always made, they are a subset of the general class of halocarbons. Haloalkanes are commonly used in industry, and as a result, they go by a variety of chemical and trade names.

Complete Step By Step Answer:
Alkyl halides (also known as haloalkanes) are alkanes that have had one or more hydrogen atoms substituted by halogen atoms (fluorine, chlorine, bromine or iodine). Haloalkanes are a class of chemical compounds made up of alkanes that contain one or more halogens. While the distinction is not always made, they are a subset of the general class of halocarbons. Haloalkanes are commonly used in industry, and as a result, they go by a variety of chemical and trade names.
Alkyl halides have a carbon-halogen bond as their functional group, with fluorine, chlorine, bromine, and iodine being the most common halogens. With the exception of iodine, these halogens have considerably higher electronegativities than carbon. As a result, as seen in the diagram on the right, this functional group is polarised, with the carbon being electrophilic and the halogen being nucleophilic. Other than electronegativity, two other features have a significant impact on the chemical activity of these compounds. The first is the strength of covalent bonds. The covalent bond between carbon and fluorine is the strongest.
This is the strongest common single bond to carbon, with a strength of about 30 kcal/mole higher than a carbon-carbon bond and about 15 kcal/mole higher than a carbon-hydrogen bond. As a result, alkyl fluorides and fluorocarbons in general are chemically and thermodynamically stable, with none of the reactivity patterns seen in other alkyl halides. The carbon-chlorine covalent bond is weaker than the carbon-carbon bond, and the bonds to the other halogens are even weaker, with the iodine bond being around 33% weaker.
The relative stability of the corresponding halide anions, which is most definitely the shape in which these electronegative atoms would be substituted, is the second element to consider. The relative acidities of the H-X acids can be used to estimate this stability, assuming that the strongest acid releases the most stable conjugate base (halide anion). All hydrohalic acids are very solid, with the exception of HF (pKa = 3.2), with minor variations in the direction HCl < HBr < HI.
Hence, option D is correct.

Note :
Alkyl halides (also known as haloalkanes) are alkanes that have had one or more hydrogen atoms substituted by halogen atoms (fluorine, chlorine, bromine or iodine). Haloalkanes are a class of chemical compounds made up of alkanes that contain one or more halogens. While the distinction is not always made, they are a subset of the general class of halocarbons. Haloalkanes are commonly used in industry, and as a result, they go by a variety of chemical and trade names.