F.6 Physics - Capacitor

This is again a standard texbook problem. You could find the solution in every physics texbook.
The charge stored in the capacitor when fully charged
= 10V uC
where V is the voltage of the battery that is used to charge up the capacitor
since there are 50 discharges in 1 second, the current = charge flow through R in 1 sceond = 50x10V uA = 500V uA = 0.5V uA
If the resistance of R is NOT small enough, you cannot be sure that there is complete discharge of the capacitor during each cycle. In this way, you cannot apply the equation, current = charge on capacitor x 50 discharges/second to calculate the current. The actual current will be much smaller than that.
In other words, the value of R should be chosen such that the time constant (RC) << 1/50 second