Initial charge on conducting sphere of radius r is Q0. If S is closed at t = 0 then charge on the sphere at any time t is
Q0e−t/4R
Q0e−t4πε0R
Q0e−t4πε0Rr
none of these
This is simply discharging of a capacitor.
∴ q=Q0e−t/CR where C=4πε0r