(a) we do not get an electric shock as we step out of our house because the original equipotential surface of open air changes, keeping our body and the ground at the same potential.
(b) yes, the man will get an electric shock if he touches the metal slab next morning. the steady discharging current in the atmosphere charge up the aluminium sheet. as a result , its voltage rise gradually. the raise in the voltage depends on the capacitance of the capacitor formed by the aluminium slab abd the ground.
(c) The occurence of thunderstorms and lightning charges the atmosphere continuously. hence, even wtih the presence of discharging current of 1800 A, the atmosphere is not discharge completely. the two opposing currents are in equilibrium and the atmosphere remains electrically neutral.
(d) during lightning and thunderstorm, light energy, heat energy , and sound energy are dissipated in the atmosphere.