Which alloy is composed of copper and zinc?

What type of oxide is aluminium oxide $(Al_2O_3)$?

Which method is used to collect $H_2$ gas in a gas jar in the laboratory?

$(a)$ Why does calcium start floating when added to water?
$(b)$ Most metals do not release hydrogen gas when reacting with nitric acid. Why?
$(c)$ Write the chemical equation for the reaction of iron with steam. Name the compound of iron obtained.

Generally,when metals are treated with mineral acids,hydrogen gas is liberated,but when metals (except $Mn$ and $Mg$) are treated with $HNO_3$,hydrogen is not liberated. Why?

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