Which block contains information about altitude?

The correct choice pertains to Block 20, which contains vital information regarding altitude. This block is specifically designated to capture and relay the aircraft's altitude data, which is crucial for air traffic control operations. Altitude information helps controllers maintain safe vertical separation between aircraft, ensuring they can manage air traffic efficiently and safely.

In the context of air traffic operations, accurate altitude reporting allows controllers to provide clearances and instructions to pilots, facilitating a structured approach to navigation and landing. Altitude data can also influence decisions about routing, delays, and collision avoidance, which are core responsibilities of air traffic controllers. Therefore, understanding and referencing the information in Block 20 is essential for safe air traffic management.