Is it possible to change the amount of memory allocated to a VM without powering it off?

In vSphere, it is indeed possible to change the amount of memory allocated to a virtual machine (VM) without needing to power it off, but this capability is dependent on certain conditions and settings. The correct choice emphasizes that there are specific memory parameters that allow for hot-add functionality.

Hot-add memory is a feature that must be enabled for the VM, and it only works with certain guest operating systems that support this feature, such as specific 64-bit versions of Windows and Linux. When hot-add memory is enabled, you can dynamically increase the memory allocation while the VM is running, thereby avoiding downtime. This capability is particularly useful in environments where uptime is critical.

The other options are less applicable in this context. For example, stating that the VM must be powered off to change memory allocation is only true for basic memory adjustments without considering advanced features like hot-add. Maintenance mode is not related specifically to adjusting memory settings either, as it refers more to performing maintenance tasks on hosts or clusters rather than individual VM memory allocation. Lastly, while there may be different types of VMs, the fundamental aspect of changing memory allocation dynamically without a power-off is primarily related to whether hot-add is supported and enabled, rather than the type of VM itself.