A dioecious flowering plant prevents both

In a dioecious flowering plant, since the unisexual flowers of different sexes are present on different plants of the same species, there is no chance for autogamy and geitonogamy.

(2) Both geitonogamy and xenogamy can be shown by plants with bisexual chasmogamous flowers and
monoecious plants.

(3) Cleistogamy is shown by unopened bisexual flowers. They show only autogamy. Bisexual chasmogamous
flowers can show autogamy, geitonogamy and xenogmy.

(4) Autogamy and xenogamy, along with geitonogamy, can be shown by bisexual chasmogamous flowers of a species.