Final answer:
The appropriate ad extension for describing features of a specific product before a click is the Structured Snippet Extension.
Step-by-step explanation:
If you want to describe features of a specific product your business offers before customers click on the ad, the correct ad extension to use is the Structured Snippet Extension. The Structured Snippet Extension allows advertisers to highlight specific aspects of their products or services by choosing a predefined header (such as Types, Brands, Styles, etc.) and listing items that fall under that header. This helps to provide context on the product's features which can help potential customers make an informed decision before they even click on the ad, possibly improving the quality of leads and click-through rates.