Which of the following represents a decimal number?

The choice that represents a decimal number is 0.25. A decimal number is a number that includes a decimal point, separating the whole number part from the fractional part. In this case, 0.25 clearly has a decimal point and indicates a value that lies between 0 and 1.

When looking at the other options, while they represent numerical values, they do not fit the criteria of being a decimal number in its conventional form. For example, 1/4 is a fraction, expressing the concept of dividing 1 into 4 equal parts. Similarly, 25% is a percentage, which represents a fraction of 100, and while it can be converted to decimal form (0.25), it is not presented as a decimal in its original form. Likewise, 2.5 is indeed a decimal number but was not selected as the answer since 0.25 precisely represents a decimal in standard form. The most straightforward and accurate representation of a decimal among the choices is 0.25.