Step 1: Idea:
Think about how a histogram is drawn: count first, then draw.
Step 2: Build a histogram in your mind.
First divide the data into bins. Then count the data points in each bin. Then draw a column for each bin.
Step 3: See which quantity is used for height.
The count (frequency) is used for height. Bin edges are used for position and width.
Step 4: Pick the option.
Option 2 names the frequency, so it is correct. The y-axis is only the scale that shows this height.
Step 5: Test every option against the result.
Option 1: The count of intervals changes how many columns appear, not how tall one is, so it fails.
Option 2: The count of points inside a bin is the height of its column, so it fits.
Option 3: The x values only show where the bins lie, so it fails.
Option 4: The y values are only the scale used to read the height, so it fails.
Step 6: Conclusion.
Option 2 is correct.
\[ \boxed{\text{Frequency of datapoints within the range}} \]