The correct answer is option 1 - Papaya.

Papaya plants have unisexual flowers, which means that separate male and female flowers are produced on the same plant. The male flowers have stamens that produce pollen, while the female flowers have ovaries that develop into fruits. This type of reproductive system is known as monoecious, where both male and female reproductive organs are present on the same plant.

Option 2 - Hibiscus, option 3 - Mustard, and option 4 - Sunflower, on the other hand, have bisexual flowers. They have both male and female reproductive organs, including stamens and pistils, within the same flower. These plants are known as hermaphroditic or bisexual.

It is important to note that while some plants have unisexual flowers, others have bisexual flowers, and some even have both types on different plants or at different times in their life cycle. Understanding the types of flowers produced by different plants helps in understanding their pollination and reproduction mechanisms.