Q.no61 .can anyone explain?

Dear Student,

As an Insulating plate passes through the plates
while Entering its Capacitance first increase C' =KC
And while Leaving its Capacitance then decreases 

Q= CV
As Capacitance increases its charge increases and On decreasing capacitance Charge also decreases.

Hence Capacitance first increase and then decrease and so the charge will.

Therefore the current outside the capacitor first flow from B to A and then from A to B

Regards