Assertion :Although geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy. Reason: In geitonogamy, pollen grains from the anthers of one flower are transferred to the stigma of another flower borne on the same plant.

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
Geitonogamy is a type of pollination in which pollen grains of one flower is transferred to the stigma of another flower belonging to either the same plant or genetically similar plant. It usually occurs in plants which show monoecious condition(unisexual male and female flowers are borne on the same plant). Thus, geitonogamy is functionally cross-pollination as it involves the pollinating agent to carry out pollination, but genetically it is similar to autogamy(self-pollination) since the pollen grains come from the genetically same plant.

So, the correct answer is 'Both Assertion and Reason are correct and Reason is the correct explanation for Assertion'.