Which of the following statements is true about CSS class selectors?

A class selector in CSS is designed to be versatile and reusable, which makes it a powerful tool for web design. The correct statement about class selectors is that they can be applied to multiple elements across a webpage. This means that you can apply the same class name to various elements, allowing for consistent styling. For example, if you define a class called "highlight" in your CSS to change the background color of elements, you can assign "highlight" to paragraphs, headings, and divs to ensure they all have the same styling without duplicating code.

This reusability of class selectors promotes efficient coding practices and makes it easier to maintain and update styles across your site. By changing one class definition, all elements with that class name are updated uniformly in terms of styling.

Other statements do not accurately express the properties of class selectors. For instance, saying a class selector can only apply to one element is incorrect; instead, it is capable of being assigned to several elements. Similarly, class selectors do not need to be unique within a page; they can be reused multiple times. Lastly, class selectors are indeed valid in CSS and are a fundamental aspect of the language, allowing for targeted styling of elements based on their assigned class attributes.