Why do scientists think that new genes arise by duplication of an original gene and divergence by mutation?

Explanation:

This is because of the fact that genomes of the organisms exhibit gene families and superfamilies. These contain genes that typically encode for proteins with similar aminoacid sequences, the proteins form by these aminoacids perform related functions. In this way the genes and their functions are duplicated among the gene families. This duplication of genes prevents the divergence from mutation.

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme

i am going to guess that it is co2.