The dehydration of alcohol follows the order:

Tertiary > Secondary > Primary

The correct answer is option 3. Tertiary > Secondary > Primary.

Let us delve into the explanation in detail:

Tertiary Alcohols: In a tertiary alcohol, the carbon bearing the hydroxyl group is attached to three alkyl groups. When this alcohol undergoes dehydration, the hydroxyl group (-OH) is removed along with a hydrogen atom from an adjacent carbon, leading to the formation of a carbocation intermediate. The resulting carbocation is stabilized by the surrounding alkyl groups through inductive and hyperconjugation effects. The alkyl groups donate electron density through hyperconjugation, stabilizing the positive charge on the carbon atom. Additionally, the inductive effect from the alkyl groups also helps stabilize the positive charge. This increased stability of the carbocation makes the dehydration of tertiary alcohols favorable, leading to a relatively high reactivity.

Secondary Alcohols: In a secondary alcohol, the carbon bearing the hydroxyl group is attached to two alkyl groups. When a secondary alcohol undergoes dehydration, a less stable carbocation intermediate is formed compared to tertiary alcohols. However, the presence of two alkyl groups still provides some stabilization to the carbocation through hyperconjugation and inductive effects, albeit to a lesser extent than in tertiary alcohols. Therefore, the reactivity of secondary alcohols in dehydration reactions is intermediate between tertiary and primary alcohols.

Primary Alcohols: In a primary alcohol, the carbon bearing the hydroxyl group is attached to only one alkyl group. When a primary alcohol undergoes dehydration, the resulting carbocation intermediate is the least stable among the three types of alcohols. The lack of additional alkyl groups to stabilize the positive charge leads to a higher energy and less favorable reaction pathway compared to tertiary and secondary alcohols. Therefore, primary alcohols exhibit the lowest reactivity in dehydration reactions among the three types of alcohols.

In summary, the reactivity order for the dehydration of alcohols is tertiary > secondary > primary, based on the stability of the carbocation intermediates formed during the reaction. This order reflects the relative ease with which the alcohols undergo dehydration to form alkenes