Assertion (A) : Endosperm is completely consumed during the development of embryo in ex-albuminous seeds. Reason (R) : Castor, pea and beans are all examples of ex-albuminous seeds.

The correct option is: "Assertion (A) is true, but Reason (R) is false."

Let us analyze the Assertion and the Reason step-by-step to understand why this option is correct.

1. Analysis of Assertion (A):
Endosperm is a nutrient-rich tissue formed during double fertilization in flowering plants, which provides nourishment to the developing embryo. In some plants, the developing embryo completely consumes the endosperm before the seed matures. Such seeds are called non-endospermic or ex-albuminous seeds. Since the endosperm is fully utilized during embryo development, matured ex-albuminous seeds do not contain any endosperm (for example, in pea, groundnut, and beans). Therefore, Assertion (A) is true.

2. Analysis of Reason (R):
The reason states that castor, pea, and beans are all examples of ex-albuminous seeds. While pea and beans are indeed ex-albuminous (non-endospermic) seeds, castor is an albuminous (endospermic) seed because its mature seeds retain a portion of the endosperm to nourish the germinating seedling. Because castor is not an ex-albuminous seed, the statement given in Reason (R) is incorrect. Therefore, Reason (R) is false.

Conclusion:
Since Assertion (A) is true and Reason (R) is false, the correct option is indeed "Assertion (A) is true, but Reason (R) is false."