Explanation:

- Correct Answer: Option 1 - An app

- Sagar Vani:

- It is a mobile application designed to disseminate ocean-related information and alerts, primarily for the benefit of coastal communities and marine stakeholders.

- Developed by the Indian National Centre for Ocean Information Services (INCOIS), it aims to provide timely updates on ocean state forecasts, advisories, and early warning information on tsunamis, storm surges, and other oceanic activities.

- Option 2: An initiative

- While Sagar Vani supports initiatives related to marine safety and awareness, it itself is not categorized solely as an initiative.

- Option 3: A scheme

- A scheme generally refers to a detailed plan or program of action, especially one related to a series of projects or tasks, which is not indicative of Sagar Vani's nature.

- Option 4: A yojana

- In the context of Indian governance, a 'yojana' is a plan or scheme usually introduced by the government, hence Sagar Vani does not fit this definition.