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 correct order of acid strength is

In the periodic table,metallic character of the elements shows one of the following trends:

The first $\left( \Delta_{i}H_{1} \right)$ and the second $\left( \Delta_{i}H_{2} \right)$ ionization enthalpies (in $kJ \ mol^{-1}$) and the $\left( \Delta_{eg}H \right)$ electron gain enthalpy (in $kJ \ mol^{-1}$) of a few elements are given below:

Elements	$\left( \Delta_{i}H_{1} \right)$	$\left( \Delta_{i}H_{2} \right)$	$\left( \Delta_{eg}H \right)$
$I$	$520$	$7300$	$-60$
$II$	$419$	$3051$	$-48$
$III$	$1681$	$3374$	$-328$
$IV$	$1008$	$1846$	$-295$
$V$	$2372$	$8581$	$+48$
$VI$	$738$	$1451$	$-40$

Which of the above elements is likely to be:
$(a)$ the least reactive element.
$(b)$ the most reactive metal.
$(c)$ the most reactive non-metal.
$(d)$ the least reactive non-metal.
$(e)$ the metal which can form a stable binary halide of the formula $MX_{2}$ ($X =$ halogen).
$(f)$ the metal which can form a predominantly stable covalent halide of the formula $MX$ ($X =$ halogen)?

How do you determine the chemical reactivity of a compound? Provide an example.

Which of the following is a metalloid?