Question

Which statement is correct for the conversion of ROH to RX by reagents
(A)$(SOC{{l}_{2}},PB{{r}_{3}},PC{{l}_{3}},P{{I}_{3}}\,and\,TsCl)$ compared to using HX?
A. No rearrangement occurs with predictable stereo – chemistry by reagent (A)
B. Reagents (A) are not useful for ${{3}^{o}}$alcohols, while HX reacts easily with${{3}^{o}}$alcohols involving no rearrangement.
C. Reagents (A) must be used in anhydrous conditions because all react vigorously with ${{H}_{2}}O$and they produce harmful gases$(S{{O}_{2}},HCl,HBr\,and\,HI)$.
D. All

Answer 1

A reagent is a chemical compound that is used to carry out certain conversions and changes the chemical composition of the reactant to form the products. It also defines the stereochemistry of the product by attacking in various ways. HX is the reagent where X is any halide, so HX is halogen acid that is a powerful reagent.

Complete answer:
We have been given certain statements regarding the conversion of alcohols to alkyl halides. These conversions are carried out by halogen acids and other reagents like phosphorus trichloride, thionyl chloride (Darzen process) etc.
Given that reagent (A) are $SOC{{l}_{2}},PB{{r}_{3}},PC{{l}_{3}},P{{I}_{3}}\,and\,TsCl$, they have no rearrangement in formation of alkyl halides, but halogen acid HX have rearrangement. So statement A is correct.
Reagent (A) is only useful for producing primary alkyl halides, but HX can be used to convert ${{3}^{o}}$ alcohols also as ${{3}^{o}}$ carbocation is highly unstable due to 3 bulky $+I$ groups. So, statement B is also correct.
The reagents (A) are used in anhydrous conditions that prevent the production of harmful gases when they react with moisture, for example $PC{{l}_{3}}+3{{H}_{2}}O\to P{{(OH)}_{3}}+3HCl$ , so this statement is also correct.
Hence, all the statements are correct.

So, the correct option is D.

Note:
To create anhydrous conditions anhydrous zinc chloride $ZnC{{l}_{2}}$ is used, it absorbs water from the products and the reaction moves in forward direction. In case of primary and secondary alcohols it is required, but not required in tertiary alcohols as the ${{3}^{o}}$ alcohol is highly reactive, so the reaction proceeds in forward direction.