What happens when a glass rod dipped in concentrated hydrochloric acid is brought near a container filled with ammonia gas?

Which substance is used for the chemical reduction of metal oxides like chromium and manganese to obtain the metal?

$A, B$ 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?

Which of the following metals is used for making jewelry?

$A$ solution of $CuSO_{4}$ was kept in an iron pot. After a few days,the iron pot was found to have a number of holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.

What is the molecular formula of sulphurous acid?