The density of gold is 19 g/cm3. If 1.9 × 10–4 g of gold is dispersed in one litre of water to give a sol having spherical gold particles of radius 10 nm, then the number of gold particles per mm3 of the sol will be
2.4 × 106
1.9 × 1012
6.3 × 1014
6.3 × 1010
