Answer: Rod X.
Explanation:
Ok, the electricity starts in the top left part. First, it must travel in the X rod, then it keeps traveling until it reaches the parallel path, and it can go to the Z rod, to the Y rod, or to both of them, and then it reaches the bulb (the circle with a X inside of it).
We know that two rods are conductors of electricity.
Now, suppose the case where rods Z and Y are the ones that conduct electricity, this means that X does not conduct electricity, then when the current reaches to X it stops (because X does not conduct) then the electricity never reaches the rods Z and Y, and then the electricity never reaches the bulb, but we know that the bulb lights up, so we must have that X is one of the conducting rods.
Then, if for example, Y does not conduct electricity, the electricity still can run through the Z rod and eventually reach the bulb.
So we can conclude that the rod that is definitely a conductor of electricity is rod X
