why dry cells are called dry while they contain water ? in electrochemistry

I wouldn't say they contained H2O but I agree they are moist. Compared to a wet cell; however, relatively speaking the dry cells are dry.

Dry cells are called "dry" because they do not contain free-flowing liquid electrolytes like traditional wet cells. Instead, they use a paste or gel-like electrolyte that contains water, but it is immobilized within the cell. This immobilized electrolyte is commonly referred to as a "semi-solid" or "moist" state rather than a liquid state. Because there is no free-flowing liquid electrolyte, dry cells are less prone to leak or spill, making them more convenient for portable applications.

To understand why dry cells are called dry, you need to consider the context in which the term is used. In electrochemistry and battery terminology, "dry" refers to the absence of a liquid electrolyte, despite the presence of water within the cell. This distinction is important because traditional wet cells, such as lead-acid batteries, use liquid electrolytes that can potentially leak or spill.

If you were researching this topic, you could go to scientific literature or textbooks on electrochemistry to learn more about the differences between dry and wet cells, how dry cells work, and the specific composition of the electrolytes used in dry cells.