Masonry arches: The voussoir placed at the crown (midpoint at the top) of an arch is known as the

Introduction / Context:
Arches are built from wedge-shaped blocks called voussoirs. Certain voussoirs have special names because of their structural role. Recognizing the “keystone” at the crown is vital for reading details and understanding load transfer in traditional masonry.

Given Data / Assumptions:

• An arch of wedge-shaped stones or bricks (voussoirs).
• The uppermost central voussoir at the crown is being identified.
• Standard arch terminology applies.

Concept / Approach:
The “keystone” is the crown voussoir that effectively locks the arch ring in place when centering is removed. The “springers” are the lowest voussoirs at the springing points; the “soffit” is the intrados surface (underside) of the arch; the “haunch” refers to the region between crown and springing, not a single block.

Step-by-Step Solution:
Identify the topmost central block → keystone.Exclude soffit (a surface), springer (lowest voussoir), and haunch (a region).Therefore choose “Key (keystone)”.

Verification / Alternative check:
Historic masonry references and drawings label the crown voussoir as the keystone, often sculpted decoratively in classical architecture.

Why Other Options Are Wrong:
Soffit: not a voussoir; it is the inner curved surface.Springer: located at the base, not the crown.Haunch: zone of the arch, not a particular block.

Common Pitfalls:
Confusing a geometric region name with the name of a voussoir; misplacing springers and keystone.

Final Answer:
Key (keystone).