The hottest part of a gas flame is the blue zone. This is because the blue zone is where the gas is burning most completely. The other zones of the flame are not as hot because the gas is not burning as completely.
The dark zone is the area closest to the burner. In this zone, the gas is not burning at all. The luminous zone is the area between the dark zone and the blue zone. In this zone, the gas is burning partially, but there is still some unburned gas. The non-luminous zone is the area beyond the blue zone. In this zone, the gas is burning completely.
The blue zone is the hottest part of the flame because it is where the gas is burning most completely. When gas burns, it combines with oxygen to form carbon dioxide and water vapor. The more complete the combustion, the more heat is produced. In the blue zone, the gas is burning so completely that there is almost no unburned gas. This means that there is very little heat lost to unburned gas, and the temperature of the flame is very high.
The other zones of the flame are not as hot because the gas is not burning as completely. In the dark zone, the gas is not burning at all. This is because there is not enough oxygen in the air to support combustion. In the luminous zone, the gas is burning partially, but there is still some unburned gas. This is because the gas is not mixing with the oxygen in the air very well. In the non-luminous zone, the gas is burning completely, but the temperature is not as high as in the blue zone because there is more unburned gas.