Which of the following is a metalloid?

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:

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

The correct order of decreasing acidic nature of oxides is:

Which of the following oxides is the most basic oxide?

What are the major differences between metals and non-metals?