Answer
An ID names one unique element; a class groups one or more elements. • An ID uses `id="name"` and should be unique on the page. • A class uses `class="name"` and can be reused. • Choose the option whose defined semantics and behavior match the task.
💡 Simple Example
<h1 id="page-title">Shop</h1><p class="note">Sale</p>
⚡ Quick Revision
Use an ID for one unique item and a class for reusable groups.