Explanation:
When a charged object is brought near a neutral object and when both of them touch each other then the neutral object also acquires the same charge that is present on the charged object.
This process of charge transfer is known as conduction.
So, when a ruler that is negatively charged touches a metal rod then the metal rod also becomes negatively charged because of conduction process.
This is because negative charge moves from the rules towards the metal rod and hence, it spreads over to the metal rod.
