Charge on the outer sphere is `q`, and the inner sphere is grounded. Then the charge `q`' on the inner sphere is q', for
`(r_(2) gt r_(1))`

Explanation

Let us suppose the charge on the inner sphere be x then the potential of the inner sphere will be `=(1)/(4iepsilon_(0))[(x)/(R_(1))+(Q)/(R_(2))]`
This potential has to be made equal to zero because the inner sphere is grounded
So, `(1)/(4piepsilon_(0))[(x)/(R_(1))+(Q)/(R_(2))]=0`
`:. x=-Q(R_(1))/(R_(2))`