Final answer:
To remove a horizontal scrollbar caused by images on smaller screens in responsive design, adjust the image dimensions with CSS properties to make them scale proportionally to the viewport size.
Step-by-step explanation:
In responsive design, if images cause a horizontal scroll bar on smaller screens, the appropriate adjustment would be to modify the image dimensions. This means you should ensure that images are not wider than the viewport of the device being used to view the content. One common method to achieve this is using CSS properties such as max-width: 100%; and height: auto; for images, which allows them to scale down proportionally to fit the screen size without causing a horizontal scrollbar.