I believe it would be the 2nd one, “increasing the area of their contact”.
The answer is A.18 let me know if you want an explanation
B. Magnesium + Hydrogen Sulfide (Reactors) ----> Magnesium Sulfide + Hydrogen (Products)
The reaction is given as
Fe2O3 (s)+ 3CO(g)--->3CO2(g)+ 2Fe(s)
No.of moles=mass in gram/molar mass
As for Fe mole =156.2g/55.847=2.7969~2.797
The ratio b/w CO and Fe is 3:2
Moles of CO needed= 2.797x3/2=4.1955
Mass of CO needed= 4.195mol x 28.01g/mol= 117.515g
