Hey!

Yes, it is true that at the temperatures below 983K, Carbon Monoxide is more effective reducing agent than carbon.

This can be proved using some equations:

1. C +O2 --CO2
2. 2CO+ O2 --2CO2
3. 2C+ 2O2 --2CO2

At the temperatures below 983K, equation (3) is more preferable because of the more negative value of ΔG. Thus, Carbon monoxide is better reducing agent.

And at temperatures above 983K, equation (1) is more preferable because ΔG is more negative. Thus, Carbon is better reducing agent.

Hope this answer helps!