We can use two quantitative “axes” that are available from the PubChem data—the (monoisotopic) molecular weight and the calculated lipophilicity (xlogP)—to separate the three pyridine derivatives. (Note that other properties such as topological PSA and H‐bond counts are identical across the three; therefore, the decisive quantitative differences come from their halogen substituent.)

Quantitative data for the three substances are as follows:

• 3‑chloropyridine  
 – Molecular weight: ca. 113.5 (monoisotopic mass ≈113.0033)  
 – xlogP: 1.3  

• 3‑bromopyridine  
 – Molecular weight: ca. 158.0 (monoisotopic mass ≈156.9527)  
 – xlogP: 1.6  

• 3‑iodopyridine  
 – Molecular weight: ca. 205.0 (monoisotopic mass ≈204.9389)  
 – xlogP: 1.8  

Since these numbers are clearly different—with the molecular weight increasing and the xlogP rising modestly as the halogen changes from Cl to Br to I—we can justify splitting these candidate substances into three groups strictly on the basis of their quantitative physicochemical data:

 Group 1 (Low MW, Lower Lipophilicity): 3‑chloropyridine  
 Group 2 (Intermediate MW, Intermediate Lipophilicity): 3‑bromopyridine  
 Group 3 (High MW, Highest Lipophilicity): 3‑iodopyridine  

Thus, using the provided quantitative PubChem values (molecular weight and xlogP), the three candidate substances fall naturally into three distinct groups.