Which of the following CSS property sets the opacity level for an element?

The correct answer is: A. opacity

The opacity property sets the opacity of an element. Opacity is a value between 0 and 1, where 0 is fully transparent and 1 is fully opaque.

The transparency property is deprecated and should not be used. It is equivalent to the opacity property with a value of 1.

The transparent keyword is a shorthand property for the opacity property with a value of 0.

Here is an example of how to use the opacity property:

css
div {
opacity: 0.5;
}

This will make the div element half transparent.