Tulip, onion, cucumber, guava, potato, brinjal, mustard, china rose – amongst these, how many have superior ovary?

The correct option is Six.

To understand why six of the given plants have a superior ovary, let us look at the classification of flowers based on the position of the ovary relative to other floral parts (calyx, corolla, and androecium) on the thalamus.

Flowers are classified into three main types based on this position:
1. Hypogynous flower: Here, the gynoecium occupies the highest position while the other parts are situated below it. The ovary in such flowers is described as superior. Examples include mustard, china rose, brinjal, potato, onion, and tulip.
2. Perigynous flower: The gynoecium is situated in the centre and other parts of the flower are located on the rim of the thalamus almost at the same level. The ovary here is half inferior. Examples include plum, rose, and peach.
3. Epigynous flower: The margin of thalamus grows upward enclosing the ovary completely and getting fused with it, and the other parts of flower rise above the ovary. The ovary is said to be inferior. Examples include guava, cucumber, and ray florets of sunflower.

Now, let us classify each of the plants listed in the question:
• Tulip: Belongs to the family Liliaceae, which has hypogynous flowers (superior ovary).
• Onion: Belongs to the family Liliaceae, which has hypogynous flowers (superior ovary).
• Cucumber: Belongs to the family Cucurbitaceae, which has epigynous flowers (inferior ovary).
• Guava: Has epigynous flowers (inferior ovary).
• Potato: Belongs to the family Solanaceae, which has hypogynous flowers (superior ovary).
• Brinjal: Belongs to the family Solanaceae, which has hypogynous flowers (superior ovary).
• Mustard: Belongs to the family Brassicaceae, which has hypogynous flowers (superior ovary).
• China rose: Belongs to the family Malvaceae, which has hypogynous flowers (superior ovary).

Counting the plants with a superior ovary (hypogynous flowers) from the list, we get:
1. Tulip
2. Onion
3. Potato
4. Brinjal
5. Mustard
6. China rose

Thus, out of the 8 plants mentioned, exactly six have a superior ovary.