Which of the following elements is a semiconductor?

Which type of oxide is $CO_{2}$?

$(a)$ What type of ores are calcined? Illustrate by giving a suitable example.
$(b)$ In what form is the calcined ore obtained,and how can it be reduced? Give chemical equations of the reduction process involved for the example provided by you.
$(c)$ Name two metals used as reducing agents by displacing metals of lower reactivity from their compounds.

Which metal ore can be concentrated by the magnetic separation method?

$A$ non-metal $X$ exists in two different forms $Y$ and $Z$. $Y$ is the hardest natural substance, whereas $Z$ is a good conductor of electricity. Identify $X$, $Y$ and $Z$.

$A, B$ and $C$ are three elements which undergo chemical reactions according to the following equations:
$A_{2}O_{3} + 2B \rightarrow B_{2}O_{3} + 2A$
$3CSO_{4} + 2B \rightarrow B_{2}(SO_{4})_{3} + 3C$
$3CO + 2A \rightarrow A_{2}O_{3} + 3C$
$(a)$ Which element is the most reactive?
$(b)$ Which element is the least reactive?
$(c)$ What is the type of reactions listed above?