Do you use the plural or singular when asking for a comparison?

If I were asked to choose between "Are your business and home addresses the same?" and "Is your business and home address the same?" I would probably choose the former because the logic of expanded question "Are your business and home addresses the same [as each other]?" seems better suited to handling both affirmative and negative answers gracefully than does the logic of the expanded question "Is your business and home address the same [as itself]?"—and easier for the site user to arrive at than the logically stronger but inferentially more difficult expansion "Is your business [address] and [your] home address [one and] the same?"

However, if I were copyediting the web page form in question, I wouldn't use either of those wordings. Instead, I would frame the question like this:

Is your business address the same as your home address?

This wording explicitly identifies what is being compared to what, with no implicit "expanded logical form" lurking in the background. A person reading the question won't spend any time at all wondering whether there's something screwy about the subject/verb agreement or about way the comparison is made.

All too often writers force themselves to consider choices in an entirely artificial either/or world in which neither choice is entirely to their liking. I recommend breaking free of those kinds of choices, on the theory that if both options are unsettling or otherwise unsatisfactory to you, they may be so to your readers as well. Look further, and you may find a better option that no one would object to.