Which of the following diagrams is known as Ishikawa diagram?

An activity diagram represents the flow of tasks or behaviors in a process or workflow and has no association with Kaoru Ishikawa or cause-and-effect analysis.

A data-flow diagram illustrates how data moves and is processed through a system during software or systems design and is entirely unrelated to Ishikawa's methodology.

A cost-benefit diagram is a financial decision-support tool used to compare projected costs against expected benefits and has no connection to Ishikawa or quality analysis.

The cause-and-effect diagram is formally known as the Ishikawa diagram, named after Japanese quality management pioneer Kaoru Ishikawa who developed it in the 1960s as part of his quality control framework. It is also widely called a fishbone diagram because of its visual resemblance to a fish skeleton, with the problem at the head and contributing causes branching off like bones. All three names - Ishikawa, fishbone, and cause-and-effect - refer to the same tool.