Which of the following is the most basic oxide?

The electronic configuration of an element is $1s^2 2s^2 2p^6 3s^2 3p^3$. What is the atomic number of the element that lies immediately below this element in the periodic table?

Which group element from the following achieves noble gas configuration after gaining two electrons?

The oxide of a metal $(R)$ can be reduced by the metal $(P)$,and metal $(R)$ can reduce the oxide of metal $(Q)$. Then the decreasing order of the reactivity of metals $(P)$,$(Q)$,and $(R)$ with oxygen is:

The type of oxide formed by the element among $Li$,$Na$,$Be$,$Mg$,$B$,and $Al$ that has the least atomic radius is $:$

Why do elements in the same group have similar physical and chemical properties?