A king orders a gold crown having a mass of 0.5 kg. When it arrives from the metalsmith, the volume of the crown is found to be 185 cm3. Is the crown made of solid gold?

The crown is not made of solid gold.  

Explanation:

Density ρ = M/V.  M and V are given.

The density of the crown is (0.5 kg)/(185 cm3) * (106 cm3)/(1 m3) = 2.7*103 kg/m3.

the answer is b, have negligible mass

force required to detach it is given by

charges are taken to be fundamental charge

now we have

so above is the minimum distance at which it will detach