B. According to the microscopic schematic diagram of gas reaction, the molecular composition of the two reactants in this conversion reaction is the same as that of CO and NO, and the molecular composition of compounds and simple substances in the product is the same as that of CO2 and N2. The relationship between the number of particles of each substance is 2: 2: 2: 1, and the equation 2CO+2NO can be used. Catalyst? . ? 2CO2+N2, so b is correct;
C, according to the characteristics of the catalyst, the catalyst can only change the reaction rate, not increase the amount of reaction products. So c is correct;
D. Comparing the changes of particles before and after the reaction, we can see that the types and atomic numbers of elements have not changed before and after the reaction, so D is correct.
So choose a.