Ferric oxide in blast furnace's upper half is mainly reduced by:

The correct option is CO (Carbon monoxide).

Step-by-Step Explanation:

1. Understanding the Blast Furnace Zones:
A blast furnace is used for the extraction of iron from its oxide ores (primarily hematite, or ferric oxide, Fe₂O₃). The furnace has a temperature gradient that ranges from approximately 2200 K at the bottom (combustion zone) to about 500 K – 800 K at the top (upper half / reduction zone).

2. Role of the Reducing Agent in the Upper Half:
As coke (carbon, C) burns at the bottom of the furnace, it forms carbon dioxide (CO₂), which reacts with more carbon to produce carbon monoxide (CO) gas. This carbon monoxide gas rises upwards through the furnace. In the upper, cooler region (temperature range of 500 K – 900 K), carbon monoxide acts as the main reducing agent. It is highly stable and active at these lower temperatures compared to solid carbon.

3. Chemical Reactions:
The ferric oxide is reduced step-by-step to iron by carbon monoxide in the upper half of the furnace through the following reactions:

First, ferric oxide is reduced to magnetite (Fe₃O₄):

$3{\mathrm{Fe}}_2{O}_3+\mathrm{CO}\to 2{\mathrm{Fe}}_3{O}_4+{\mathrm{CO}}_2$

The magnetite is then reduced further to iron (Fe) or iron(II) oxide (FeO):

${\mathrm{Fe}}_3{O}_4+4\mathrm{CO}\to 3\mathrm{Fe}+4{\mathrm{CO}}_2$

Similarly, any remaining ferric oxide is reduced to iron(II) oxide:

${\mathrm{Fe}}_2{O}_3+\mathrm{CO}\to 2\mathrm{FeO}+{\mathrm{CO}}_2$

Therefore, in the upper half of the blast furnace, the reduction of ferric oxide is predominantly carried out by carbon monoxide (CO) gas rather than solid carbon (C).