Final answer:
The magnification of Bacillus subtilis at 1000x is 1000 times larger than its actual size.
Step-by-step explanation:
The magnification of Bacillus subtilis at 1000x is 1000 times larger than its actual size. This means that if the actual size of Bacillus subtilis is, for example, 5 µm, it would appear as 5000 µm (or 5 mm) when observed under a microscope at 1000x.