Which of the following represents an improper fraction?

An improper fraction is defined as a fraction where the numerator is greater than or equal to the denominator. Looking at the given options, the fraction 3/2 has a numerator (3) that is greater than its denominator (2), which meets the criteria for being an improper fraction.

In contrast, the fraction 37/39 has a numerator that is less than the denominator, making it a proper fraction. The mixed number 6 3/4 is a combination of a whole number and a proper fraction, and therefore does not qualify as an improper fraction. Lastly, the fraction 1/2 also has a numerator that is less than the denominator, classifying it as a proper fraction as well. Thus, 3/2 is the only fraction listed that is deemed improper.