In which case can a firearm be used legally in self-defense?

Using a firearm in self-defense is legally justified when there is a reasonable belief of imminent danger to life or safety. This means that the individual perceives an immediate threat that puts them or others at risk of serious harm or death. The legal principle behind this is to allow individuals the right to protect themselves when faced with a clear and present danger.

The emphasis on "reasonable belief" means that the perception of danger must be based on circumstances that a typical person would recognize as threatening. The law typically examines both the situation and the mindset of the person using the weapon to determine whether the use of force was justifiable.

While having a registered firearm or being instructed by law enforcement may play a role in the legalities of firearm ownership and use, they don't directly relate to the justification of using a firearm in self-defense. Similarly, being on private property is not a definitive factor; self-defense laws apply regardless of location, provided the circumstances of the threat align with legal standards.