Hi @Mehul_Sanghvi,
Welcome to the MongoDB Community forums 
There’s no any specific Atlas-side mechanism to limit the number of connections by IP.
However, you can use maxPoolSize option in connection string to limit the number of connection in the connection pool. The default value is 100 .
May I ask, why you specifically intend to do that?
As per my understanding, the application’s client gracefully uses a connection from the pool, and return it once its purpose is served. No explicit closure of connections is necessary, thereby sparing the application from the overhead of repeatedly creating and closing connections, is an expensive operation.
Best regards,
Kushagra