Write two observations for the following chemical reaction:
$(a)$ Potassium iodide solution is added to lead nitrate solution.

Name the type of reaction for the following:
$(i)$ Silver items turning black when left exposed to air.
$(ii)$ Change in colour of copper sulphate from blue to green on dipping an iron nail in it.

Write true or false for the following statement:
During endothermic reactions,heat is transferred from the reacting substances to the surroundings.

List two observations which you record while burning magnesium in air.

$A$ metal $P$,when exposed to moist air for a longer period of time,loses its shiny brown surface and gains a green coat. Why has this happened? Identify the metal. Write the name and chemical formula of this green-coloured compound. List two ways to prevent this process.

Write a balanced chemical equation for each of the following reactions and also classify them.
$(a)$ Iron $(III)$ oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
$(b)$ Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.