The correct answer is option 'B' - 7.

The sternum is a hard, plate-like structure that forms the ventral (underside) part of the body wall of insects. It provides support and protection for the internal organs. In female cockroaches, the sternum is present on the abdomen.

Here is a detailed explanation of the number of sternum present at the abdomen of a female cockroach:

1. Anatomy of the Cockroach:
The body of a cockroach is divided into three main regions - head, thorax, and abdomen. The abdomen is the posterior part of the body and consists of 10 segments. Each segment is covered by a hard exoskeleton called a tergum dorsally (on the upper side) and a sternum ventrally (on the underside).

2. Number of Sternum in Cockroach:
In a female cockroach, the abdomen has seven sternum plates. These sternum plates are present on the ventral side of the abdomen, between the segments.

3. Arrangement of Sternum Plates:
The sternum plates in the abdomen of a female cockroach are arranged in a specific pattern. Starting from the first segment of the abdomen, the sternum plates are numbered as follows:
- The first segment does not have a sternum plate.
- The second segment has a single sternum plate.
- The third and fourth segments have a pair of sternum plates each.
- The fifth, sixth, and seventh segments also have a single sternum plate each.

Therefore, the total number of sternum plates in the abdomen of a female cockroach is seven.

4. Purpose of Sternum:
The sternum plays a crucial role in supporting and protecting the internal organs of the cockroach. It provides attachment points for muscles and acts as a shield for the delicate organs present in the abdomen.

In conclusion, the correct answer is option 'B' - 7. The female cockroach has seven sternum plates present on the abdomen, providing support and protection to the internal organs.

Abdomen in both male and female consists of 10 segment..10 tergal plates are found and 9 sternal plates are foundas 10th sternum is absent

IN males all 9 sterna are visible but in females only 7 are visible

coz IN females 7th sternum is boat shaped shaped 7th 8th 9th sternum together form brood pouch . 7th sternum covers 8and9 th sterna....

if the question is about number of sternum visible in female cockroach answer is (b)i.e7