Rg is solved by finding the thinnest possible carbon nanotube, and it turns out you can do it the way I thought of involving surface area and area density of granite.
Not impressed with the questions this month. Copper and Silver were poor, Gold gave you no hint to increase your significant figures if you had an answer nearby and Rg was unnecessarily confusing.
At the minute I am working out the volume of the nanotube by doing Lr^2pi, (50500x(0.2x10-9)^2x3.14159...) and then dividing this value by the mass density of graphene, which I have found to be 1315 g per m^2. Am I on the right lines and getting one of my values wrongs or am I not on the right track?
Oh jeez, this Rg is driving me insane! I think I've found all the values but I get something in the *10^-8 region, which I assume is far too small. Also, where are the values of "50.5" and "50500" coming from for length? Shortest distance between england and france that I get is 34km?