How many countries does Mexico border?

Is it three? We do not have to list them but am I right in saying they are the U.S., Belize and Guatemala

You're right.

Yes, you are correct. Mexico borders three countries: the United States to the north, Belize to the southeast, and Guatemala to the south. If you want to find the answer to this question on your own, you can use various resources such as an atlas, a map, or even an internet search.