You have an application named App1 that listens for incoming requests on a preconfigured group of 50 TCP ports and UDP ports. You install App1 on 10 Azure virtu...

Azure Application Gateway is limited to 100 active listeners that are routing traffic. Active listeners = total number of listeners - listeners not active.
If a default configuration inside a routing rule is set to route traffic (for example, it has a listener, a backend pool, and HTTP settings) then that also counts as a listener.
Note: Azure Application Gateway is a web traffic load balancer that enables you to manage traffic to your web applications.
Application Gateway can make routing decisions based on additional attributes of an HTTP request, for example URI path or host headers. This type of routing is known as application layer (OSI layer 7) load balancing.
Incorrect:
Not B: Floating IP. Some application scenarios prefer or require the same port to be used by multiple application instances on a single VM in the backend pool.
Common examples of port reuse include:
clustering for high availability
network virtual appliances
exposing multiple TLS endpoints without re-encryption.
Not D: Multiple site hosting enables you to configure more than one web application on the same port of application gateways using public-facing listeners. It allows you to configure a more efficient topology for your deployments by adding up to 100+ websites to one application gateway. Each website can be directed to its own backend pool.
Reference:
https://github.com/MicrosoftDocs/azure-docs/blob/main/includes/application-gateway-limits.md