In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate,a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available,which of the following can be used in place of lead nitrate?

The following diagram displays a chemical reaction. Observe it carefully and answer the following questions:
$(a)$ Identify the type of chemical reaction that will take place and define it. How will the colour of the salt change?
$(b)$ Write the chemical equation of the reaction that takes place.
$(c)$ Mention one commercial use of this salt.

$A$ substance $X$, which is an oxide of a group $2$ element, is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution which turns red litmus blue. Identify $X$ and write the chemical reactions involved.

Give reasons for the following:
$(i)$ All decomposition reactions are endothermic reactions.
$(ii)$ Colour of copper sulphate solution changes when an iron nail is dipped in it.
$(iii)$ Respiration is an exothermic reaction.

Why is a combustion reaction considered an oxidation reaction?

Translate the following statements into chemical equations and then balance them.
$(a)$ Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
$(b)$ Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.