Solution:
To apply a style to exactly one element on a web page, configure a css ID.
The id attribute specifies a unique id for an HTML element (the value must be unique within the HTML document). The id value can be used by CSS and JavaScript to perform certain tasks for a unique element with the specified id value.
It is known as identifiers (IDs) are lexical tokens that name entities. Identifiers are used extensively in virtually all information processing systems. Identifying entities makes it possible to refer to them, which is essential for any kind of symbolic processing.
Thus the right answer is id.
