Which of the following CSS Property sets the stacking order of positioned elements?

x-index
y-index
z-index
all of the mentioned

The correct answer is C. z-index.

The z-index property is a CSS property that specifies the stacking order of positioned elements. The higher the z-index value, the higher the element will appear in the stacking order.

The x-index and y-index properties are not valid CSS properties.