Which alloy is composed of copper and zinc?

When a metal $X$ is treated with cold water,it gives a basic salt $Y$ with molecular formula $XOH$ (Molecular mass $= 40$) and liberates a gas $Z$ which easily catches fire. Identify $X, Y, Z$.

Out of the two metals $P$ and $Q$, $P$ is less reactive than $Q$. Suggest an activity to arrange these metals in the order of their decreasing reactivity. Support your answer with a suitable chemical equation.

State whether the following statement is true or false:
The elements or compounds,which occur naturally in the earth's crust,are known as minerals.

Which of the following metals are obtained by electrolysis of their molten chlorides?
$(i) Na, (ii) Ca, (iii) Fe, (iv) Cu$

Which metal is the least reactive?