In which plants do outbreeding devices prevent autogamy but not geitonogamy?

For a dioecious plant,which of the following is true?

What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?

Match the following contrivances from Column-$I$ with their examples in Column-$II$.

Column-$I$	Column-$II$
$i$. Protandry	$a$. Calotropis
$ii$. Prepotency	$b$. Tobacco
$iii$. Self sterility	$c$. Sunflower
$iv$. Herkogamy	$d$. Apple

This is a genetic mechanism that prevents self-pollination by inhibiting pollen germination or pollen tube growth in the pistil,thereby preventing fertilization.

Match the following columns regarding plant breeding systems and select the correct option:
Column-$I$: $(i)$ Monoecious, (ii) Dioecious
Column-$II$: $(p)$ Prevents both autogamy and geitonogamy, $(q)$ Prevents autogamy but not geitonogamy
Column-$III$: $(x)$ Papaya and Date palm, $(y)$ Castor and Maize