"Are" or "Is" when linking two singular nouns in a sentence?

When you are talking about about two singular nouns and link them together in a sentence with a conjunction such as "and" which verb form is correct?

For example, would you say "Where is the broom and mop?" or "Where are the broom and mop?"

If the two are considered as a unit, you use the singular verb:

• Where is the pestle and mortar?
• Mumford and sons is my favourite band.

However, when each noun is considered to be a separate unit, you use a plural verb:

• My sister and my mother keep contradicting me.
• The battery and the engine seem to have died.

Unless you really consider a broom and a mop together to be a single unit, you shouldn't use them with a singular verb. Also, repeat the definite article the. If you say the broom and mop, it looks like a single unit just as it does with a pestle and mortar. If you say the broom and the mop it is clear that they are two different objects:

Where are the broom and the mop?