What conditions are necessary for alkenes to react with water?

The reaction of alkenes with water, specifically in the context of hydration to form alcohols, requires specific conditions to proceed effectively. The correct answer mentions that steam at 300°C and a catalyst are necessary.

The high temperature of 300°C is critical because it provides the energy needed to overcome the activation energy barrier of the reaction, facilitating the formation of the alcohol from the alkene. Additionally, using steam ensures that water is in sufficient quantity to drive the reaction forward.

The presence of a catalyst, typically an acid such as phosphoric acid, is essential as it increases the reaction rate without being consumed in the process. It helps in forming the more reactive carbocation intermediate from the alkene, which then quickly reacts with water to form the desired alcohol.

In contrast, the other options either lack the necessary high temperature combined with a catalyst or are unsuitable for this particular reaction. Therefore, the requirement for steam, high temperature, and a catalyst directly correlates with the effective and efficient conversion of alkenes to alcohols.