Answer
(c) $30\% $ deficiency of air
Work Step by Step
If a fuel is burned with $70$ percent theoretical air, it means that the actual amount of air used is only $70$ percent of the air required for complete combustion. In other words, there is a deficiency of air compared to the theoretical requirement. This implies that the combustion process is not optimized and some of the fuel may not burn completely due to insufficient oxygen.
