Which of the following is a block that restricts train movement based on signals?

The term "Absolute Block" refers specifically to a block that is used to completely restrict train movement to ensure safety. In railway operations, an absolute block means that no trains are allowed to enter that section of track unless the signal indicates that it is safe to do so. This is critical in preventing collisions and managing train traffic effectively.

The effectiveness of absolute blocks comes from the signaling system that governs them. When a signal is in a 'stop' position, it indicates to the locomotive engineer that the block is occupied or unsafe for travel, hence restricting any train from entering. Only when the area is clear and the corresponding signal changes, can trains safely proceed into that block. This system is a fundamental component of safe railway operations, ensuring that trains do not enter occupied tracks, thereby maintaining overall safety and efficiency in train movements.

Other options do not convey the same level of restriction or purpose. Controlled blocks, for example, may allow some level of movement based on specific conditions, and "Extra Train" does not pertain to block signaling but rather refers to supplementary or additional train movements. Hence, the understanding of the absolute block's role in restricting movement based on signals makes it the correct selection in this context.