Which of the following acts as a catalyst in the production of ammonia by Haber's process?

Which of the following properties is generally not shown by metals?

$A, B$ 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?

If copper is kept open in air,it slowly loses its shining brown surface and gains a green coating. It is due to the formation of

Which of the following options is correct according to the reactivity of metals?

Which alloy is composed of copper and zinc?