"Saturated hydrocarbons burn with a blue flame while unsaturated hydrocarbons burn with a sooty flame".Why??

saturated hydrocarbon burns with a blue flame becoz it ubdergoes complete combustion.While the unsaturated ydrocarbon burns with a yallow sooty flame becoz combustion is not complete since the amount of carbon content is more than the hydrogen content and hence carbon is not completely bunt and become a sooty deposit.

I think that your book is actually saying the percentage of carbon in unsaturated hydrocarbon is more than saturated hydrocarbon. Let's take the hydrocarbon with two carbon, which are saturated hydrocarbon(ethane), unsaturated hydrocarbons(ethene and ethyne).

The percentage of carbon in ethane(C2H6CX2HX6) =[2(12)/2(12) + 6(1)]⋅100[2(12)/2(12) + 6(1)]⋅100 = 80 %

The percentage of carbon in ethene(C2H4CX2HX4) =[2(12)/2(12) + 4(1)]*100[2(12)/2(12) + 4(1)]*100 = 86 %

The percentage of carbon in ethyne(C2H2CX2HX2) =[2(12)/2(12) + 2(1)]⋅100[2(12)/2(12) + 2(1)]⋅100 = 92 %

According from above, we can see unsaturated hydrocarbon have a higher percentage of carbon than saturated hydrocarbon. So, there is a sooty flame when burning unsaturated hydrocarbons and a clean flame when burning saturated hydrocarbon

I think that your book is actually saying the percentage of carbon in unsaturated hydrocarbon is more than saturated hydrocarbon. Let's take the hydrocarbon with two carbon, which are saturated hydrocarbon(ethane), unsaturated hydrocarbons(ethene and ethyne).

The percentage of carbon in ethane(C2H6CX2HX6) =[2(12)/2(12) + 6(1)]⋅100[2(12)/2(12) + 6(1)]⋅100 = 80 %

The percentage of carbon in ethene(C2H4CX2HX4) =[2(12)/2(12) + 4(1)]*100[2(12)/2(12) + 4(1)]*100 = 86 %

The percentage of carbon in ethyne(C2H2CX2HX2) =[2(12)/2(12) + 2(1)]⋅100[2(12)/2(12) + 2(1)]⋅100 = 92 %

According from above, we can see unsaturated hydrocarbon have a higher percentage of carbon than saturated hydrocarbon. So, there is a sooty flame when burning unsaturated hydrocarbons and a clean flame when burning saturated hydrocarbon.

I thing it help you.