An activity is characterized as abnormally dangerous when it creates a foreseeable risk of serious harm even when reasonable care is taken. This definition aligns with the principles of strict liability in tort law, which applies to those activities that pose inherent dangers and risks that cannot be completely mitigated by the exercise of ordinary care.
For example, activities such as blasting or using harmful chemicals are considered abnormally dangerous because they can lead to significant harm irrespective of how careful one may be. The legal system recognizes that such activities carry an elevated potential for harm and therefore imposes strict liability on those engaging in them, meaning they can be held responsible for any resulting damages, regardless of whether they acted negligently.
The other options don't capture the essence of what makes an activity abnormally dangerous. While negligence must be established in standard tort cases (as suggested by the first option), this is not applicable for abnormally dangerous activities. The third option suggests these activities are inherently harmful, but it misses the key point that liability is about the inability to fully manage risks through precautions. The fourth option, relating to legality, is irrelevant because the characterization is based on the nature of the activity and its risks, not its legality in various jurisdictions.