Which altitude is the lowest at which an intersection can be determined, depicted with the letter 'R' on a chart?

The correct answer is Minimum Reception Altitude (MRA). This altitude indicates the lowest height at which an aircraft can receive navigational signals from a nearby VOR (VHF Omnidirectional Range) or other navigational aids for the purpose of determining its position over a specific intersection. The depiction of the intersection with the letter 'R' serves as a reminder for pilots that they must be at or above the MRA to ensure reliable signal reception.

Choosing MRA is crucial for flight safety, as it guarantees that pilots have access to the necessary navigation information when they are near an intersection. The other options, while all important altitudes in air navigation, do not specifically relate to the ability to effectively receive navigational signals and determine intersections on a chart. Minimum Crossing Altitude pertains to the lowest altitude at which specific waypoints can be crossed, Minimum En Route Altitude refers to the lowest altitude used for en route navigation that ensures terrain clearance, and Maximum Authorized Altitude denotes the upper limit for safe flight levels but does not address navigational signal reception.