Diagram:

$\begin{aligned} \text{Wt. of oxygen} &= \text{wt. of oxygen needed } – \text{wt. of oxygen present} \\ &= 2.66 – 0.1 \\ &= 2.56 kg \\ \end{aligned}$

$\text{Wt. of air required for complete combustion}$

$\begin{aligned} &= \text{[Air contains 23% } O_2 \text{ by weight ]} \\ 2.56 \times 100 / 23 &= 11.13 \text{kg per 1 kg of coal} \\ \text{Air required for 2 kg of coal} &= 11.13 \times 52 \\ &= 22.26 kg \end{aligned}$

Answer: Weight of air required = 22.26 kg