Which of the following is a mixed number?

A mixed number is defined as a whole number combined with a proper fraction. In this case, the correct answer is a mixed number because it consists of the whole number 16 and the proper fraction 1/2.

The other options do not fit this definition: 3/4 is a proper fraction, 2.5 is a decimal representation and can be expressed as a mixed number but isn't in that form, and 7 is a whole number without any fractional component. Thus, 16 1/2 is the only option that combines both a whole number and a fraction, making it the correct choice.