Which of the following property is used to increase or decrease how bold or light a font appears?

The correct answer is D. font-weight.

The font-weight property is used to increase or decrease how bold or light a font appears. It takes a value from 100 to 900, where 100 is the lightest and 900 is the heaviest. The default value is 400.

The font-family property is used to specify the font family that should be used for the element. The font-style property is used to specify the style of the font, such as italic or normal. The font-variant property is used to specify the variant of the font, such as small caps or normal.

Here is an example of how to use the font-weight property:

css
p {
font-weight: bold;
}

This will make all paragraphs in the document appear in bold.