Which of the following is(are) an endothermic process(es)?
$(i)$ Dilution of sulphuric acid
$(ii)$ Sublimation of dry ice
$(iii)$ Condensation of water vapours
$(iv)$ Evaporation of water

Explain the type of reactions represented by the following equations:
$(i)$ $Mg + CuSO_4 \longrightarrow MgSO_4 + Cu$
$(ii)$ $NH_4NO_2 \longrightarrow N_2 + 2H_2O$

$A$ magnesium ribbon is burnt in oxygen to give a white compound $X$ accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen,it continues to burn and forms a compound $Y.$
$(a)$ Write the chemical formulae of $X$ and $Y.$
$(b)$ Write a balanced chemical equation,when $X$ is dissolved in water.

On heating blue coloured powder of copper $(II)$ nitrate in a boiling tube,copper oxide (black),oxygen gas and a brown gas $X$ is formed.
$(a)$ Write a balanced chemical equation of the reaction.
$(b)$ Identify the brown gas $X$ evolved.

$A$ small amount of quicklime is added to water in a beaker.
$(a)$ Name and define the type of reaction that has taken place.
$(b)$ Write the balanced chemical equation for the above reaction. Write the chemical name of the product obtained.
$(c)$ State two observations that you will make in the reaction.

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.