Answer: 25N
method: total force in the right hand direction is 100N and total force in the left hand direction is 125N. To get the net force, we add forces if they are in the same direction and substract if they are in opposite directions. since 100N and 125N are in opposite directions, we substract the larger value from the smaller value. Then we get 25N in the left hand direction as the final answer.
The answer is A) accumulation zone
Silver is a very good conductor, this means its resistivity is very low (from table, we can check the precise value, which is

).
Pure water, instead, is a very bad conductor, this means its resistivity is very high, of order of

(

). Even without knowing the precise value of the pure water resistivity, we can estimate the ratio between the pure water resistivity and the silver resistivity by comparing the two orders of magnitude:

Therefore, we can say that the correct answer is