What do the numbers 3 and 4 refer to in 3nh4?

3 nitrogen atoms and 12 hydrogen atoms

Explanation: In a chemical equation, number represents the atoms present. Number at the base of the atom must be multiplied with the number written at the first atom for example 3NH4 so here for Hydrogen 4 is multiplied with 3 i.e. 12Hydrogen but for first atom Nitrogen only 3 is there so 3 nitrogen and 12 Hydrogen is present.

47

explanation:

ok

answer; ///(b) it is composed of four protein chains and four heme groups;