What are the main functions of client operating system, and how does it differ from a server operating system?

The OS that operates within the desktop or various devices which obtain services from a server. It is mainly used for personal use computers and the OSs are Microsoft, Mac.
But the server OS is used on servers, and it is mainly used in big organisations or enterprises, and the OSs are windows server, Redhat, Linux

What is EBS volume and mention their types?

Amazon EBS (Elastic Block Store) provides block-level storage that you can attach to EC2 instances.
Think of it like a virtual hard drive for your cloud server.
EBS volumes are mainly categorized into SSD and HDD types:

Mention the volumes of HDD and SSD.

SSD - gp2, gp3, io1 / io2
HDD - st1 & sc1

What is the difference between the Root volume and Non-Root volume?

The root volume contains the OS files needed to start the EC2 instance.
Non-root volume is Extra EBS volumes attached to the instance.

What is the difference between public key and private key?

The difference between a public key and a private key is most commonly explained in the context of EC2 key pairs, which are used for secure instance access (SSH / RDP)