Answer:
1. in lac operon; gene activity is induced when lactose is present in the medium, whereas in case of trp operon, repression of the gene activity takes place in presence of tryptophan in the medium.
2. lac operon spans about 4-6kb...whereas trp operon spans abut 7kb.
3. lac operon helps in the breakdown of lactose into glucose and galactose, to generate energy( catabolic pathway ) in case of trp operon, it helps in the synthesis of enzymes required for the formation of the amino acid Tryptophan( anabolic pathway ).
4. lac operon is an example of positive regulation ; and trp operon is an example of negative regulation.
Trp operon is also regulated by other mechanism called attenuation while no such even occurs in lac operon . .