Q5:When do we need persistent connections in our application?

Why is option©: To reduce the load on the server incorrect.
As explained during an online multiplayer game if a lot of requests are made every now and then , this could cause load in the server resulting in high latency which is why Persistent connection becomes important.

@Abhas_Upadhayay Persistent connections do not necessarily reduce the load on the server. Though they cut down the latency of the response. This is why they are preferred in apps with high read-writes. There is a limit to the open connections a server can handle.