A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?

Which among the following is (are) double displacement reaction(s)?

$\left(\mathrm{i}\right) \mathrm{Pb}+{\mathrm{CuCl}}_2\to {\mathrm{PbCl}}_2+\mathrm{Cu}$

$\left(\mathrm{ii}\right) {\mathrm{Na}}_2{\mathrm{SO}}_4+{\mathrm{BaCl}}_2\to {\mathrm{BaSO}}_4+2\mathrm{NaCl}$

$\left(\mathrm{iiii}\right) \mathrm{C}+{\mathrm{O}}_2\to {\mathrm{CO}}_2$

$\left(\mathrm{iv}\right) {\mathrm{CH}}_4+2{\mathrm{O}}_2\to {\mathrm{CO}}_2+2{\mathrm{H}}_2\mathrm{O}$

Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by the liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is are true about slaking of lime and the solution formed?

(i) It is an endothermic reaction.

(ii) It is exothermic reaction.

(iii) The $\mathrm{pH}$ of the resulting solution will be more than seven.

(iv)The $\mathrm{pH}$ of the resulting solution will be less than seven.

Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?

$\left(\mathrm{i}\right)$ Displacement reaction

$\left(\mathrm{ii}\right)$ Precipitation reaction

$\left(\mathrm{iii}\right)$ Combination reaction

$\left(\mathrm{iv}\right)$ Double displacement reaction

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