Group-13 elements react with O2 to form oxides of type M2O3. Which among the following is the most basic oxide?

🧠 Going down Group 13, oxide nature shifts: acidic → amphoteric → basic. Tl is the heaviest, so its oxide is the most basic The element's metallic character increases as you descend. More metallic atom → more ionic M–O bonding → more basic oxide. Tl sits at the bottom of Group 13 in Period 6 — most metallic, most basic oxide.

🗺️ Classify each Group 13 oxide $\ce{B2O3}$: B is a metalloid leaning non-metal. Acts like an acidic oxide (gives boric acid in water). $\ce{Al2O3}$: Al sits on the metal-non-metal boundary. Amphoteric — reacts with both acid and base. $\ce{Ga2O3}$: similar to Al. Mostly amphoteric. $\ce{Tl2O3}$: Tl is fully metallic (Period 6). Behaves like a typical metal oxide. Most basic of the four.

⚠️ The trap Many students pick $\ce{Al2O3}$ because Al is taught as a metal at school level. But Al's oxide is the textbook amphoteric example, not a strongly basic one. The "most basic" label belongs to the heaviest member — Tl. Always pick the bottom-of-the-group oxide when the question says "most basic" within a group.

$\boxed{\text{Answer: (c)}}$