First, let's see how 23 compares with the squares of the positive whole numbers on the number line.
1² = 1
2² = 4
3² = 9
4² = 16
5² = 25
The value of 23 is right between the square of 4 and the square of 5. Thus, the value √23 will be between 4 and 5.
Since 23 is much, much closer to the square of 5 than the square of 4, we can assume that the value √23 will be closer to 5 on the number line than 4.
Look at the attached image to see where I plotted the approximate location of √23.
You will realize that this approximation is pretty close since the actual value is roughly 4.80.
Let me know if you need any clarifications, thanks!