To arrange the amines in decreasing order of basicity, we compare the availability of the lone pair on nitrogen.

However, the question statement provided here does not include the structures/formulae of compounds I, II, and III. Without knowing what I, II, and III actually are, the order of basicity cannot be derived from first principles.

Step 1: What determines basicity of amines?

For amines, basicity depends mainly on:

1. Electron-donating or electron-withdrawing groups attached to nitrogen
2. Resonance delocalization of the lone pair
3. Hybridization of nitrogen
4. Steric hindrance affecting protonation/solvation
5. Aromatic vs aliphatic character

In general:

• Aliphatic amines are usually more basic than aniline-like amines.
• If the lone pair is involved in resonance, basicity decreases.
• Electron-donating groups increase basicity.
• Electron-withdrawing groups decrease basicity.

Step 2: Limitation in the given data

The actual compounds labeled I, II, and III are missing from the prompt. Therefore, a rigorous option-by-option derivation is not possible from the supplied information alone.

Step 3: Compare with stored answer

The stored correct answer is B, which corresponds to:

$\text{III} > \text{I} > \text{II}$

Since the structural information is absent, I cannot independently verify this ordering from chemistry principles using the given prompt alone.

Conclusion

Because the identities of I, II, and III are not shown, the problem is incomplete in the provided form. So I cannot confidently derive the order myself.

If the intended structures were available in the original question image/text, then the order might indeed be option B, but that cannot be established from the current data.