The correct answer is: barium is a good absorber of X-rays and this helps the stomach to appear clearly in contrast with the other regions in the picture.

Barium compounds, such as barium sulfate, are commonly used in X-ray examinations of the digestive system, including the stomach. Barium sulfate is an opaque substance that does not easily dissolve in water, making it suitable for use in medical imaging.

When a patient ingests a barium preparation before an X-ray examination of the stomach, the barium coats the lining of the stomach, providing a contrast medium for the X-ray images. Barium is a good absorber of X-rays, meaning it blocks or attenuates the passage of X-rays through the body. This allows the radiologist to clearly visualize the shape, size, and condition of the stomach as the X-rays are absorbed or scattered differently by the barium-coated stomach lining compared to the surrounding tissues.

By using barium as a contrast agent, the radiologist can better identify abnormalities, such as tumors, ulcers, or structural issues in the stomach, as they will appear clearly in contrast to the surrounding tissues in the X-ray images.

It`s important to note that barium is not transparent to X-rays, as stated in the first option. Instead, it acts as an absorber of X-rays, enhancing the visibility of the stomach in the X-ray images.