Among $$Al_2O_3, SiO_2, P_2O_3$$ and $$SO_2$$ the correct order of acid strength is

he correct increasing order of acidic strength among the oxides of third-period elements: Aluminum ($$\text{Al}$$), Silicon ($$\text{Si}$$), Phosphorus ($$\text{P}$$), and Sulfur ($$\text{S}$$).

1. Periodic Trend of Oxide Nature

As you move from left to right across a period in the periodic table, the electronegativity of the elements increases.

• Elements with lower electronegativity (metals) form basic or amphoteric oxides.
• Elements with higher electronegativity (non-metals) form acidic oxides.

Therefore, across Period 3, the acidic nature of oxides increases significantly from left to right

Hence, 

Arranging them in increasing order of their acidic strength gives:

$$\text{Al}_2\text{O}_3 < \text{SiO}_2 < \text{P}_2\text{O}_3 < \text{SO}_2$$ i.e. Option B