Among ${\text{Al}}_2{\text{O}}_3,{\text{SiO}}_2,{\text{P}}_2{\text{O}}_3$ and ${\text{SO}}_2$ the correct order of acid strength is:

In a period, the acidity of oxides increases from left to right as the non-metallic character increases.${\text{Al}}_2{\text{O}}_3$ is amphoteric.${\text{SiO}}_2$ is weakly acidic.${\text{P}}_2{\text{O}}_3$ is acidic.${\text{SO}}_2$ is strongly acidic.
Order: ${\text{Al}}_2{\text{O}}_3<{\text{SiO}}_2<{\text{P}}_2{\text{O}}_3<{\text{SO}}_2$.