In which of the following are the elements in the correct order of their chemical reactivity in terms of oxidizing property?

The diagonal relationship between $Be$ and $Al$ is due to:

Which of the following sets of elements have the strongest tendency to form anions?

Given below are two statements:
Statement-$I$: Along the period,the chemical reactivity of the elements gradually increases from group $1$ to group $18$.
Statement-$II$: The nature of oxides formed by group $1$ elements is basic,while that of group $17$ elements is acidic.
In the light of the above statements,choose the most appropriate answer from the options given below:

The increasing order of reactivity among group-$1$ elements is $Li < Na < K < Rb < Cs$ whereas that among group-$17$ elements is $F > Cl > Br > I$. Explain.

The size of $Be^{2+}$ and $Al^{3+}$ is not so close,but they show a diagonal relationship due to: