On adding dilute hydrochloric acid to copper oxide powder,the solution formed is blue-green. Predict the new compound formed which imparts a blue-green colour to the solution.

Giving chemical equations,answer the following:
$(a)$ What happens when copper is heated in air?
$(b)$ What happens when the product obtained in the above reaction is heated in hydrogen?

$A$ 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.

Explain the type of reaction represented by the following equation:
$(i) \ CuSO_{4} + 2NaOH \longrightarrow Cu(OH)_{2} + Na_{2}SO_{4}$

Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is

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