Which attribute is used to specify that a link should be opened in a new tab?

The attribute that is used to specify that a link should be opened in a new tab is the target attribute with the value "_blank". This is a standard practice in HTML, where setting the target attribute to "_blank" instructs the browser to load the linked document in a new window or tab, depending on the user's browser settings and preferences.

Using target="_blank" is quite common when web developers want to allow users to view additional content without navigating away from the current page. This creates a seamless user experience by letting users explore links while keeping the original page accessible.

The other options do not conform to standard HTML practices for opening links in new tabs. For instance, href="_new" does not have the desired effect as it lacks context and specification to link to a new tab or window. Similarly, rel="external" is intended for indicating the relationship of the linked resource as external, but it does not control the behavior of the link. Lastly, link="newtab" is not a recognized HTML attribute and does not serve any function in opening links in a new tab.