- a) the number of molecules in a mole [= gram-molecular-weight not Talpa europea yeh daftie]
- b) 6.02 x 1023 if you can manage superscripts <sup>23</sup> in HTML
- c) calculators often render this as 6.02e+23
- d) 6.02 ^ 23 is also acceptable to sciency ppl
- e) 602,214,080,000,000,000,000,000
But these are all hard to interpret in audio mode, so there Avogadro's number is 602 sextillion. Seems that until recently Système International SI units had no official prefixes for numbers larger than 1024 or smaller than 10-24. But stellar distances and computer storage is driving to agree terms for counts larger than this. For a while ten years ago, different teams were pushing for the adoption of Hellabyte or Brontobyte for 1027 bytes but this got side-eye from the SI Metrology committee because the one letter abbreviations H for henry the unit of electrical conductance and B for byte were already spoken for; and that would lead to needless confusion.
quetta Q 10^30 ** quecto q 10^-30
ronna R 10^27 ** ronto r 10^-27
yotta Y 10^24 ** yocto y 10^-24
zetta Z 10^21 ** zepto z 10^-21
exa E 10^18 ** atto a 10^-18
peta P 10^15 ** femto f 10^-15
tera T 10^12 ** pico p 10^-12
giga G 10^9 ** nano n 10^-9
mega M 10^6 ** micro μ 10^-6
kilo k 1,000 ** milli m 0.001
hecto h 100 ** centi c 0.01
deka da 10 ** deci d 0.1
As a camel is said to be a horse designed by a committee, the SI General Conference on Weights and Measures has delivered a bit of a kludge. For the higher / more recent designations there is a neat symmetry: Q R Y Z reflects q r y z. But P peta 1015 is not the reciprocal of p pico10-12 nor is M mega 106 the reciprocal of m milli 10-03.
And I can tell you that μ for micron is a typographical disaster for students and scientists being far too frequently replace by u or "mu". But my annoyance is really focused on making two-letter da the official SI abbreviation for deka when the most recent meeting redoubled the precedent for capitals being big Q R Y Z with l.c. letters being q r y z. Historical inertia has fixed k for kilo and h for hecto rather than K and H. No room for complacency here.