Final answer:
The easiest method for separating the subunits of botulinum protein is size-exclusion chromatography, which is ideal for differentiating molecules based on size.
Step-by-step explanation:
The easiest method to separate the two subunits of the botulinum protein for subsequent analytical purposes would be size-exclusion chromatography. This technique, also known as gel filtration chromatography, separates molecules based on their size, which is ideal for separating protein subunits with different molecular weights. Other methods like gas chromatography, mass spectrometry, and thin-layer chromatography are not as well-suited for this purpose because they are designed for other types of analyses or require the proteins to be volatile or in a non-protein form.