What is rancidity? Mention any two ways by which rancidity can be prevented?

$(i)$ When a metal $X$ is added to the salt solution of a metal $Y$,the following chemical reaction takes place: Metal $X +$ Salt solution of $Y \rightarrow$ Salt solution of $X +$ Metal $Y$.
$(ii)$ Mention the inference you draw regarding the reactivity of metal $X$ and $Y$ and also about the type of reaction. State the reason for your conclusions.

What happens when zinc granules are treated with dilute solutions of $NaCl$ and $NaOH$? Also,write the chemical equations if a reaction occurs.

Which one of the following processes involves chemical reactions?

$A$ silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
$(a)$ Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
$(b)$ Name the black substance formed and give its chemical formula.

State whether the following statement is true or false:
Calcium oxide is also called lime or quicklime.