A research Van de Graaff generator has a $2\mathrm{.}30$ m diameter metal sphere with a charge of $42\mathrm{.}0$C on it$.$

$($a$)$

What is the potential $($in kV$)$ near its surface?

kV

$($b$)$

At what distance from its center $($in m$)$ is the potential $125$ kV$?$

m

$($c$)$

An oxygen atom with three missing electrons is released near the Van de Graaff generator. What is its kinetic energy in keV at the distance found in part $($b$)?$

keV