Final answer:
The tool and key combination that create a perfect square selection is the "Rectangular Marquee Tool" along with the "Shift" key held down while dragging.
Step-by-step explanation:
To create a perfect square selection, use the "Rectangular Marquee Tool" in software like Adobe Photoshop. By default, this tool creates rectangular selections. However, by pressing and holding the "Shift" key while dragging the cursor, the selection shape is constrained to a perfect square. This happens because the "Shift" key maintains an aspect ratio of 1:1, ensuring equal width and height in the selection.
For instance, when using the "Rectangular Marquee Tool" without holding the "Shift" key, dragging the cursor will allow you to freely select a rectangular area. However, if you press and hold the "Shift" key while dragging, the selection will maintain an equal width and height, thereby creating a perfect square selection.
This combination is particularly useful for tasks requiring symmetrical or precisely shaped selections, such as cropping images to square dimensions or isolating specific portions for editing while ensuring uniformity.