Q1: __________ fuels require the maximum percentage of 'excess air' for complete combustion.

ANS:A - Solid

Among the options provided, solid fuels generally require the maximum percentage of 'excess air' for complete combustion. Solid fuels, such as coal or wood, typically have a complex composition and structure, which can make it difficult to achieve complete combustion. The presence of impurities, varying densities, and uneven distribution of oxygen within the solid fuel can lead to incomplete combustion if sufficient oxygen is not supplied. Therefore, solid fuels often require a higher percentage of excess air (more oxygen than theoretically required for complete combustion) to ensure that all fuel components have enough oxygen for complete oxidation. So, the correct answer is "Solid".