Assertion (A) Zirconium can be purified by van Arkel method.
Reason (R) $\mathrm{ZrI}_4$ is volatile and decomposes at 1800 K .
Assertion (A) Sulphide ores are concentrated by froth flotation method.
Reason (R) Cresols stabilise the froth in froth floatation method.
Assertion (A) Zone refining method is very useful for producing semiconductors.
Reason (R) Semiconductors are of high purity.
Assertion (A) Hydrometallurgy involves dissolving the ore in a suitable reagent followed by precipitation by a more electropositive metal.
Reason (R) Copper is extracted by hydrometallurgy.
Explain the following
(a) $\mathrm{CO}_2$ is a better reducing agent below 710 K whereas CO is a better reducing agent above 710 K.
(b) Generally sulphide ores are converted into oxides before reduction.
(c) Silica is added to the sulphide ore of copper in the reverberatory furnace.
(d) Carbon and hydrogen are not used as reducing agents at high temperatures.
(e) Vapour phase refining method is used for the purification of Ti .
(a) As shown in Ellingham diagram which relates Gibbs free energy and temperature at below 710 K.
$\Delta G_{\left(\mathrm{C}, \mathrm{CO}_2\right)}<\Delta \mathrm{G}_{(\mathrm{C}, \mathrm{CO})} \mathrm{~So}, \mathrm{CO}_2$ is a better reducing agent than CO while above 710 K it becomes a very good reducing agent.
(b) Generally, sulphide ores are converted to oxides before reduction as reduction of oxides can easily be done using C or CO depending upon metal ore and temperature.
(c) Silica is a flux added to the sulphide ore of copper in the reverberatory furnace leading to the formation of slag
$\mathrm{FeO}+\mathrm{SiO}_2 \rightarrow \underset{\text { Slag }}{\mathrm{FeSiO}_3}$
(d) Carbon and hydrogen are not used as reducing agents at high temperature. At high temperature carbon and hydrogen readily form their carbides and hydrides respectively.
(e) Vapour phase refining method is used for the purification of Ti as
$$\mathrm{Ti}+2 \mathrm{I}_2 \xrightarrow{523 \mathrm{~K}} \mathrm{TiI}_4 \xrightarrow{1700 \mathrm{~K}} \mathrm{Ti}+2 \mathrm{I}_2$$