Which type of block is characterized by one recessed end and three smooth shells?

The block characterized by one recessed end and three smooth shells is known as a corner block. This type of block is specifically designed for use at the corners of masonry walls, where it facilitates a smooth transition and helps to maintain structural integrity. The recessed end allows for better alignment and bonding with adjacent blocks, which is crucial in achieving a sturdy wall structure. Additionally, the three smooth shells of the corner block contribute to its aesthetic appeal while providing a solid framework for the corners, where additional stress and weight are often concentrated. Understanding the function and design of the corner block is essential for masonry work, especially in ensuring that corners are both functional and visually cohesive.