`Ba^(2+)` ions are poisonous, still they are provided to patients before taking stomach X-ray. Explain.

Explanation

A barium meal (suspension of `BaSO_4` in water) is generally given to the patients when X-ray photographs of the alimentary canal are required. The salt provides a coating of the alimentary canal and hence X-ray photograph can be taken since it is quite transparent to the X-ray otherwise. `BaSO_4` is almost insoluble in water and hence it does not pass from digestive system to the circulatory systen and can therefore be safety used for the purpose.