Selected intern's day-to-day responsibilities include: 1. Monitor and manage multiple WhatsApp groups. 2. Engage with group members through timely responses and valuable content. 3. Implement a performance management system to track engagement metrics. 4. Develop strategies to increase group participation and interaction. 5. Collaborate with the marketing team to align group activities with overall company goals. 6. Provide regular reports on group performance and suggest improvements. 7. Stay up to date on industry trends and best practices for community management.