When viewed under a compound light microscope on low power, the letter "p" will appear upside down and reversed.

Here's why:

* Compound microscopes use two lenses: An objective lens (close to the specimen) and an eyepiece lens (what you look through).

* The objective lens creates a real, inverted image: This means the image is flipped both vertically and horizontally.

* The eyepiece lens magnifies the image further: But it doesn't change the orientation.

So, the letter "p" is flipped both vertically and horizontally, making it appear as a "d".