Comparing acid strength of oxoacids derived from oxides Acidic strength has been compared before here and here, but the first question is about organic chemistry (and I am talking about inorganic chemistry), and the second does not discuss molecules such as $\ce{Cl2O7}$, $\ce{P4O10}$, $\ce{CO2}$, $\ce{N2O5}$, $\ce{Al2O3}$ etc. These molecules do not contain hydrogen. So what are the factors which affect their acid or base strength?
The following question brings me this doubt:

Which of the following is the correct order of acidic strength?
(A) $\ce{Cl2O7}$ &gt; $\ce{SO2}$ &gt; $\ce{P4O10}$
(B) $\ce{CO2}$ &gt; $\ce{N2O5}$ &gt; $\ce{SO3}$
(C) $\ce{Na2O}$ &gt; $\ce{MgO}$ &gt; $\ce{Al2O3}$
(D) $\ce{K2O}$ &gt; $\ce{CaO}$ &gt; $\ce{MgO}$
The question quoted in the OP is designed to test a periodic table trend concept.  

Particularly, within a given row of the periodic table, excluding noble gases, the element oxides form increasingly acidic aqueous solutions from left to right across the row.  

See the lecture by Dr. Pinkington The Acid-Base Character of Oxides and
Hydroxides in Aqueous Solution for additional information. 

Only answer (A) is increasingly acidic left to right across the periodic table.