Dioecious species have separate male and female plants, which means that they cannot self-pollinate (autogamy) because an individual plant only produces either male or female flowers. Therefore, we can definitely rule out options (P) and (Q) as possible modes of pollination in the case of kiwi:
(P) cleistogamous autogamy - ruled out because it involves self-pollination, which is not possible in a dioecious species.
(Q) chasmogamous autogamy - ruled out for the same reason as (P).
On the other hand, the remaining options are still possible:
(R) geitonogamy - This involves pollination between flowers of the same plant, but it doesn't necessarily require self-pollination. If there are both male and female flowers on a single plant (although not typical for dioecious species), geitonogamy could occur.
(S) xenogamy - This involves pollination between flowers of different plants, which is a possible mode of pollination in dioecious species. Pollen from a male plant can be transferred to a female plant by a pollinator, leading to xenogamy.
So, the correct answer is:
(c) only Q and S