Which property of an oxide changes from basic to acidic across period 3?

1. Period 3 starts with metals like Na and Mg on the left. 2. Metal oxides such as Na₂O and MgO are basic in nature. 3. The middle element Al gives Al₂O₃, an amphoteric oxide. 4. Non-metal oxides on the right such as P₂O₅, SO₃ and Cl₂O₇ are acidic. 5. So the acid-base character of the oxide changes from basic to acidic. 6. The change reflects falling metallic character across the period. _Source: Selina Concise Chemistry ICSE Class 10, Ch 1 'Periodic Table' (aplustopper.com extract)_