While on duty, when can an armed guard carry a firearm?

The correct answer is based on the regulations surrounding the carrying of firearms by armed guards, which require that they only carry the caliber specified on their permit. This is a critical safeguard that ensures that the guard is trained and compliant with the legal parameters set by governing authorities regarding the types of firearms they are authorized to carry.

The stipulation to carry only the caliber mentioned on their permit ensures familiarity and proficiency with that specific firearm, reducing the risk of mishandling or illegal use. This adherence to the specifics of the permit fosters responsibility and accountability among armed personnel.

In contrast, options suggesting the ability to carry any caliber firearm or a firearm of any type do not align with these legal requirements and could create significant liabilities or safety issues, as those firearms could be outside the guard's approved training or experience. The option that mentions carrying a firearm issued by their employer might seem plausible, but it does not directly address the necessity of adhering to the caliber specified in the guard's permit, which is essential for compliance with the law.