Ok, here it goes. Hydrogen, oxygen and carbon make up about 99% of the average human. I'm going to cheat a little and leave out the other 1%, which is made up of trace elements (that is, stuff there's only a trace of in the body). Then, let's assume an average adult weighs 70 kilograms. Be sure to keep in mind that the following numbers are based on the number of atoms, not percent of body weight (by weight we are mostly oxygen). A 70 kg body would have approximately 7*1027 atoms. That is, 7 followed by 27 zeros:
7,000,000,000,000,000,000,000,000,000
Of that, 4.7*1027 would be hydrogen atoms, which have one proton and one electron each. Another 1.8*1027 would be oxygen, which has 8 protons, 8 neutrons and 8 electrons. There are 7.0*1026 carbon atoms, which have 6 protons, 6 neutrons and 6 electrons. Now, let's add that all up:
Protons Neutrons Electrons
Hydrogen 4.7*1027 0 4.7*1027
Oxygen 1.4*1028 1.4*1028 1.4*1028
Carbon 4.2*1027 4.2*1027 4.2*1027
Total 2.3*1028 1.8*1028 2.3*1028
Well, you'll have to agree that really is a whole bunch.
Answer 2
As they say in French - "Beaucoup," meaning a lot! A very technical, but very interesting, discussion of this can be found at http://www.foresight.org/Nanomedicine/Ch03_1.html. In summary, for a typical human of 70 kg, there are almost 7*1027 atoms (that's a 7 followed by 27 zeros!) Another way of saying this is "seven billion billion billion." Of this, almost 2/3 is hydrogen, 1/4 is oxygen, and about 1/10 is carbon. These three atoms add up to 99% of the total!
I don't think so. I think technical limitations will keep it an oddity.