The following reactions take place in the blast furnace in the preparation of impure iron. Identify the reaction pertaining to the formation of the slag.

• ${\mathrm{Fe}}_2{\mathrm{O}}_3 \left(\mathrm{s}\right) + 3\mathrm{CO}\left(\mathrm{g}\right) \to 2\mathrm{Fe}\left(\mathrm{l}\right)\hspace{0.17em}+ 3{\mathrm{CO}}_2\left(\mathrm{g}\right)$

• ${\mathrm{CaCO}}_3\left(\mathrm{s}\right) \to \mathrm{CaO}\left(\mathrm{s}\right)\hspace{0.17em}+ {\mathrm{CO}}_2\left(\mathrm{g}\right)$

• $\mathrm{CaO}\left(\mathrm{s}\right) + {\mathrm{SiO}}_2\left(\mathrm{s}\right) \to {\mathrm{CaSiO}}_3\left(\mathrm{s}\right)$

• $2\mathrm{C}\left(\mathrm{s}\right) + {\mathrm{O}}_2\left(\mathrm{g}\right) \to 2\mathrm{CO}\left(\mathrm{g}\right)$

Consider the following equation, which represents a reaction in the extraction of chromium from its ore

$2{\mathrm{Fe}}_2{\mathrm{O}}_3·{\mathrm{Cr}}_2{\mathrm{O}}_3 + 4{\mathrm{Na}}_2{\mathrm{CO}}_3 +3{\mathrm{O}}_2 \to 2{\mathrm{Fe}}_2{\mathrm{O}}_3+ 4{\mathrm{Na}}_2{\mathrm{CrO}}_4+ 4{\mathrm{CO}}_2$

Which one of the following statements about the oxidation states of the substances is correct?

• The iron has been reduced from +3 to + 2 state.

• The chromium has been oxidised from +3 to +6 state.

• The carbon has been oxidised from +2 to +4 state.

• There is no change in the oxidation state of the substances in the reaction.

Dipping iron article into a strongly alkaline solution of sodium phosphate

• does not affect the article

• $\mathrm{Fr}o\mathrm{m} {\mathrm{Fe}}_2{\mathrm{O}}_3·{\mathrm{xH}}_2\mathrm{O} \mathrm{on} \mathrm{the} \mathrm{surface}$

• forms iron phosphate film

• forms ferric hydroxide

Apatite is an ore of

• fluorine

• chlorine

• bromine

• Iodine

Which of the following electrolytes is least effective in causing flocculation of ferric hydroxide sol?

• K₂[Fe(CN)₆]

• K₂CrO₄

• KBr

• K₂SO₄

To dissolve argentite ore which of the following is used?

• Na[Ag(CN)₂]

• NaCN

• NaCl

• HCl

Calamine is

• CaCO₃

• MgCO₃

• ZnCO₃

• CaCO₃ + CaO

The purest zinc is made by

• electrolytic refining

• zone refining

• the van Arkel method

• the Mond process

German silver does not contain

• Sn

• Cu

• Zn

• Ni

TiI₄  on heating gives 

• TiI₂ + I₂

• Ti + 2I₂

• TiI₃+ 1/2 I₂

• None of these