Which scenario describes the use of a deadly weapon in a crime?

In this scenario, the use of a firearm in a robbery clearly illustrates the use of a deadly weapon in the commission of a crime. A firearm is classified as a deadly weapon because it has the capacity to cause death or serious bodily harm. When used in a robbery, the firearm serves to threaten or intimidate the victim, thereby exacerbating the seriousness of the offense and increasing the potential for violence.

The other options describe situations that do not meet the definition of using a deadly weapon in a criminal context. Cutting a rope with a knife does not constitute a crime, especially since there's no indication of malicious intent or harm. The use of a kitchen appliance defensively implies a protective rather than aggressive action, and using a harmless object in a prank does not involve a weapon at all or any intent to cause injury, thus removing it from the context of criminal activity involving a deadly weapon.