Which of the following compounds is most acidic?

Which of the following represents the correct order of acidic strength?

Given below are two statements:
Statement $I$: Chlorine can easily combine with oxygen to form oxides,and the product has a tendency to explode.
Statement $II$: Chemical reactivity of an element can be determined by its reaction with oxygen and halogens.
In the light of the above statements,choose the correct answer from the options given below.

In known elements,the maximum number is of

Which of the following orders of acidic strength is correct?

Which of the following is an amphoteric oxide?