What happens when a target in a target group fails health checks in an ALB?

Based on your configured threshold it marked as a unhealthy

What is the main advantage of using an Application Load Balancer over a Classic Load Balancer?

Application load Balancer HTTP/HTTPS feature that provide smart routing better flexibility and modern application support

Which ELB type operates at Layer 7 (Application layer) of the OSI model?

Application load Balancer

Which load balancer supports host-based and path-based routing?

Application load balancer HTTP protocols

What are the two main components of Auto Scaling?

Scaling in/out