Measurements on sodium have provided the following data: resistivity 4.7 × 10 8 ohm m, Hall coefficient -2.5× 10 -10 m³ coulomb -1, critical wavelength of transparency 210 nm, and density 971 kb/m³. Calculate (i) the density of electrons, (ii) the effective mass, (iv) the collision time, (v) the number of electrons per atom available for conduction. Electric conduction in sodium is caused by electrons. The number of atoms in a kg mole is 6.02×1026 and the atomic weight of sodium is 23.