Final answer:
The compounds NaCl, Cl2, and HCl should be listed as NaCl (highest electronegativity difference due to its ionic bonding), followed by HCl (polar covalent bonding), and Cl2 (nonpolar with zero electronegativity difference). NaCl2 does not exist as a simple chemical compound.
Step-by-step explanation:
The question asks us to list the following compounds in decreasing electronegativity difference: NaCl, Cl2, HCl, and NaCl2. First, we note that Cl2 is nonpolar and thus will have an electronegativity difference of zero. NaCl will have the largest difference because it is an ionic compound formed between a metal (Na) and a nonmetal (Cl), where sodium has an electronegativity (EN) of 0.93 and chlorine has an EN of 3.16.
HCl has polar covalent bonding with hydrogen having an EN of 2.20 and Cl has an EN of 3.16, leading to an electronegativity difference of 0.96. The compound NaCl2 does not exist in simple chemistry, but if it did hypothetically, the electronegativity difference would again be significant due to the Na-Cl interaction. Based on this, the correct order ignoring the compound NaCl2, which seems to be an error, would be NaCl > HCl > Cl2.