Final answer:
When two 5g point charges are placed on 1m long threads, the phenomenon observed is electrostatic repulsion.
Step-by-step explanation:
The phenomenon observed when two 5g point charges are placed on 1m long threads is electrostatic repulsion. This means that the charges will push each other away due to the repulsive force between them.
Electrostatic forces are long-range forces that act over large distances and can be either attractive or repulsive, depending on the charges involved.