Which of the following fractions is classified as an improper fraction?

An improper fraction is defined as a fraction where the numerator is greater than or equal to the denominator. In this case, 3/2 fits this definition since 3, the numerator, is greater than 2, the denominator.

The other options consist of proper fractions, where the numerator is less than the denominator. For example, 1/4 has a numerator of 1, which is less than the denominator of 4, making it a proper fraction. Similarly, both 2/6 and 4/5 have numerators (2 and 4, respectively) that are also less than their corresponding denominators (6 and 5, respectively), thereby classifying them as proper fractions as well.

Thus, 3/2 stands out as the only improper fraction in the list.