Question

Why do vegetables release water when salt is added to them ?

Answer 1

cucumber is release water when salt is added to them

Answer 2

The principle is Osmosis. The skin acts as a semi permeable membrane and water has a tendency to flow from lower salt concentration to higher salt concentration to equalise the salt concentrations.

Thus, when you add salt, the concentration outside goes high and water will start releasing out, to balance the salt strength inside the vegetable and outside.