Correct answer is option 4 inches.
The minimum length of a saw – cut prism is 4 inches. The length of a masonry prism may be reduced by saw – cutting. Prisms composed of regular shaped hollow units shall have at least one complete cell with one full width cross web on either end.
Prisms composed of irregular shaped units shall be cut to obtain as symmetric a cut as possible and the minimum length of a saw – cut prisms shall be 4 inches (102mm).