Which of the following oxides is the most basic oxide?

Given below are two statements:
Statement $I$: The number of pairs among $[Al_2O_3, Cr_2O_3]$, $[Cl_2O_7, Mn_2O_7]$, $[Na_2O, V_2O_3]$ and $[CO, N_2O]$ that contain oxides of same nature (acidic, basic, neutral or amphoteric) is $4$.
Statement $II$: Among $Na_2O, Al_2O_3, CO$ and $Cl_2O_7$, the most basic and acidic oxides are $Na_2O$ and $Cl_2O_7$, respectively.

Show by a chemical reaction with water that $Na_{2}O$ is a basic oxide and $Cl_{2}O_{7}$ is an acidic oxide.

Which of the following is the correct order of gradually decreasing basic nature of the oxides?

$Be$ and $Al$ show similarities in properties due to diagonal relationship except in the property $X$ given below. What is $X$?

The chemical properties of $Li$ and $Mg$ are similar because: