Please explain experts.....

Dear Student,
 
Methods or devices which favor cross pollination are known as outbreeding devices. Plants have developed methods to prevent self pollination.
Autogamy is prevented by following ways:

• Pollen release and stigma receptivity not coordinated
• Different positioning of the anther and the stigma
• Production of unisexual flowers

Ways to prevent both autogamy and geitonogamy:

• Presence of male and female flowers on different plants, such that each plant is either male or female (dioecy).
• This mechanism is present in several species of papaya.

Monoecious plant means one flower has only one reproductive organ in them ie.. male or female. so they cannot undergo pollination within the same flower ( autogamy) but they can undergo pollination with different flowers of the same plant (geitonogamy )
Hence, option 3 is incorrrect.

Regards