Which of the following elements is a semiconductor?

Out of the $114$ elements discovered so far,how many elements do not behave as metals?

What is the color of a potassium dichromate solution?

What is the chemical formula of sodium sulfite?

What is ammonium hydroxide $(NH_4OH)$?

$(a)$ Consider the following chemical equation:
$Fe_{2}O_{3} + 2Al \rightarrow Al_{2}O_{3} + 2Fe$
Name two categories in which you can place this reaction.
$(b)$ Define the term 'Oxidation' of a substance and name the substance oxidised and the oxidising agent in the above reaction.