How do you properly write a block altitude?

To properly write a block altitude, the format should indicate a range between two altitudes where an aircraft is allowed to operate. The lower altitude is stated first, followed by the letter "B" indicating the lower limit for the block, and then the upper altitude. This convention helps ensure clarity about the airspace boundaries and the specific altitude range allowed for aircraft to operate.

In this case, writing it as "100B150" clearly communicates that the aircraft is authorized to fly at any altitude between 100 and 150. This format is standard in aviation communication to avoid confusion in air traffic control and is essential for maintaining safe separation between aircraft at different altitudes.

The other options do not adhere to the correct format. For instance, using "150B100" implies a block ranging from 150 down to 100, which could lead to misunderstandings regarding the altitude limits. Similarly, "200A250" indicates an altitude range in a way that does not fit the standard procedure, as "A" is not used in block altitude representations. Lastly, “75B125” might represent a block, but the numbers are not typical for airspace, since 75 is below standard flight altitudes.