The correct answer is C. Virtualization.

According to CompTIA A+ Core 1 220-1201 objectives under Networking and Cloud/Virtualization Concepts:

Virtualization allows a single physical server to host multiple virtual machines (VMs), each running its own operating system and applications.

This reduces hardware costs because fewer physical servers are required to run multiple workloads, and it improves resource utilization, scalability, and management.

Why the other options are incorrect:

A. Containerization: Optimizes application deployment by packaging applications and dependencies, but containers share the host OS kernel and are not full OS instances.

B. Cloud computing: Refers to delivering computing services over the internet; it can use virtualization but is broader and not specifically focused on reducing physical hardware.

D. Remote desktop services: Provides remote access to desktops or applications; it does not reduce hardware requirements for hosting multiple OS environments.