Explanation:
12N by first law of newton is net force after colloision
If net external force acting on the system is zero, momentum is conserved. That means, initial and final momentum are same → total momentum of the system is zero.
THIS IS NOT THE EXACT ANSWER BUT IT MIGHT HELP
The cover slips serves two purposes: (1) it protects the microscope's objective lens from contacting the specimen, and (2) it creates an even thickness (in wet mounts) for viewing.
B.strong but weaker than the weak force