Final answer:
The Web Designer is responsible for creating the landing page mockup in a RACI chart. Their role centers on designing the visual and functional aspects of websites, which includes mockups.
Step-by-step explanation:
In a completed RACI chart, which stands for Responsible, Accountable, Consulted, and Informed, various roles are defined in regard to specific tasks and deliverables within a project. When it comes to the creation of a landing page mockup, the Web Designer is typically responsible. This is because the Web Designer's primary role involves the visual and functional aspects of websites, including layout, user interface, and user experience design. Thus, they are the ones who take charge of producing design mockups in alignment with the project's goals. The Project Manager oversees and coordinates the project, ensuring all parts align with the overall objectives. The Content Writer would provide the text for the website, and the Quality Assurance Tester would be responsible for testing the site for issues before it goes live.