The slag formed in the blast furnace during the extraction of iron from haematite is:

$CaO$  reacts with the impurities of ore called gangue particles  to form slag. Slag is the mixture of $CaSi{O}_3$ and $Ca(Al{O}_2{)}_2$.Slag is a useful byproduct. It is usedin road making, cement manufacturing a light weight building materials.

$Flux+gangue\to Slag$
$CaO+Si{O}_2\to CaSi{O}_3$
$CaO+A{l}_2{O}_3\to Ca(Al{O}_2{)}_2$

Hence option B is correct.