zinc will react with sulphuric acid forming zinc sulphate dissolved in solution and releasing hydrogen gas.
Zn + conc. 2 H2SO4 ZnSO4 + SO2 + 2 H2O

Riemann's green is a green pigment ZnO.CoO, which is obtained by heating a mixture of zinc oxide and cobalt nitrate or by the reaction of cobalt nitrate with either 3Zn(OH)2ZnCO3 or zinc sulphate.

SinceECu2+/CuECu2+/Cuhas a greater positive value thanEH+/HEH+/H, the reaction that is feasible at the cathode is

Cu2+(aq)+2eCu(s)

Number of beats (n) =f2- f1

= 256 - 250

= 6 beats /sec