The correct option is Option A: A, C, D.

Let's analyze each statement:

A. All GAs are acidic in nature.

This statement is true. Gibberellins (GAs) are a group of plant hormones that are primarily known for their role in stem elongation, seed germination, and flowering. Their chemical structure features a characteristic carboxyl group (COOH), making them acidic.

B. Auxins are antagonists to GAs.

This statement is false. While auxins and GAs can have opposing effects in some cases, they generally act synergistically, meaning they work together to enhance each other's effects. For example, both auxins and GAs can promote stem elongation, and their combined action can result in more pronounced growth than either hormone alone.

C. Zeatin was isolated from coconut milk.

This statement is true. Zeatin is a naturally occurring cytokinin, a class of plant hormones that promote cell division. It was first isolated from coconut milk, a rich source of plant growth regulators.

D. Ethylene induces flowering in Mango.

This statement is true. Ethylene, a gaseous plant hormone, plays a crucial role in fruit ripening and can also induce flowering in certain plant species, including Mango. Ethylene treatment can be used to synchronize flowering in Mango trees, leading to more efficient fruit production.

E. Abscisic acid induces parthenocarpy.

This statement is false. Abscisic acid (ABA) is a plant hormone primarily known for its role in stress responses, such as drought tolerance and dormancy. It does not induce parthenocarpy, which is the development of fruit without fertilization. Parthenocarpy can be induced by other hormones, such as auxins and gibberellins, depending on the plant species.

Therefore, the correct statements are A, C, and D, making Option A the correct choice.