Answer:
 a
  The volume charge density is  [tex]\rho = nq[/tex]
b
  The surface charge density is  [tex]\sigma = n^{\frac{2}{3} } q[/tex]
Explanation:
From the question we are told that
  The radius is  R
   The length is L
    The velocity is  v
    The number of ions per unit volume is  n
     The charge is  q
     The thickness of the cylinder surface is  [tex]n^{\frac{1}{3} }[/tex]
The volume charge density is mathematically represented as
   [tex]\rho = nq[/tex]
The surface charge density is mathematically represented as
  [tex]\sigma = \rho n^{\frac{1}{3} }[/tex]
substituting for  [tex]\rho[/tex]
   [tex]\sigma = n * n^{\frac{1}{3} } q[/tex]
   [tex]\sigma = n^{\frac{2}{3} } q[/tex]
