Answer:
To prepare cyclohexene from cyclohexanol, the most suitable method is the use of concentrated phosphoric acid (H3PO4). This method is commonly known as the acid-catalyzed dehydration of alcohols. Let's understand why this method is the best choice.

Dehydration of Alcohols:
The dehydration of alcohols is a reaction that involves the removal of a water molecule from the alcohol molecule to form an alkene. In this case, cyclohexanol is dehydrated to form cyclohexene.

Role of Concentrated Phosphoric Acid (H3PO4):
Concentrated phosphoric acid serves as a catalyst in this reaction. It provides the necessary acidic conditions for the elimination of water from the alcohol. Phosphoric acid is a strong acid and can readily donate a proton, making it an effective catalyst for this reaction.

Explanation:
Here is a step-by-step explanation of the reaction using concentrated phosphoric acid:

1. The cyclohexanol molecule reacts with a proton (H+) from the phosphoric acid, forming a cyclohexanol cation (oxonium ion) and a phosphate anion.
C6H11OH + H3PO4 → C6H11OH2+ + H2PO4-

2. The oxonium ion is unstable and undergoes a rearrangement to form a more stable alkene intermediate called cyclohexyl cation.
C6H11OH2+ → C6H11+ + H2O

3. The phosphate anion acts as a base and abstracts a proton from the cyclohexyl cation to form cyclohexene and regenerate the phosphoric acid catalyst.
C6H11+ + H2PO4- → C6H10 + H3PO4

4. The final product of the reaction is cyclohexene, which is obtained by the elimination of water from cyclohexanol.

Advantages of Using Concentrated Phosphoric Acid:
- Concentrated phosphoric acid is readily available and relatively inexpensive.
- It is a mild acid and does not cause extensive side reactions or unwanted by-products.
- The reaction can be carried out at moderate temperatures, making it suitable for the conversion of alcohols to alkenes without excessive decomposition of the starting material or the product.

Conclusion:
In conclusion, the best method to prepare cyclohexene from cyclohexanol is by using concentrated phosphoric acid (H3PO4) as a catalyst. This method provides the necessary acidic conditions for the dehydration of the alcohol, resulting in the formation of cyclohexene as the desired product.