$12.$ Regarding the Earth and a cloud layer $800$ m above the Earth as the "plates" of a capacitor, calculate the

capacitance if the cloud layer has an area of $1\mathrm{.}0$ km$2$

$.$ If an electric field of $2\mathrm{.}0106$

N$/$C makes the air break

down and conduct electricity $($lightning$),$ what is the maximum charge the cloud can hold?