Which of these features ensure that VMs are not disrupted in case a host goes down?

The correct answer is VMware HA because it is specifically designed to provide high availability for virtual machines. When enabled in a vSphere environment, VMware HA monitors the health of the host systems. In the event that a host fails, VMware HA automatically restarts the virtual machines that were running on that host on other available hosts in the cluster. This minimizes downtime and ensures that virtual workloads remain operational despite hardware failures.

vMotion, while integral to resource management and load balancing, allows for live migration of VMs between hosts without downtime but does not inherently provide protection against host failures. VMware DRS is focused on resource allocation and balancing loads among hosts, ensuring VMs get the resources they need but similarly does not handle host failures directly. The vSphere Client is a management interface and has no functional role in ensuring VM uptime during host outages.