Final answer:
BiCl₃ has more acidic properties than NCl₃ because BiCl₃ is a lewis acid able to accept electron pairs, whereas NCl₃ acts as a lewis base and does not behave as an acid.
Step-by-step explanation:
When comparing acidic properties of BiCl₃ (bismuth trichloride) and NCl₃ (nitrogen trichloride), one must consider the electronegativity and stability of the molecules. Bismuth is lower on the periodic table than nitrogen which generally indicates that as you go down a group, acidity increases. However, NCl₃ does not exhibit acidic behavior because nitrogen in NCl₃ has no hydrogen atoms to donate, which is a typical property of an acid. Instead, NCl₃ acts as a lewis base. On the other hand, BiCl₃ is a lewis acid due to the vacant d orbitals that can accept electron pairs, in addition to the fact that bismuth is more metallic than nitrogen. Therefore, BiCl₃ is the one with more acidic properties.