On a Cisco IOS device, which command is used at the user EXEC prompt to gain access to higher-level, privileged EXEC mode commands?

Introduction / Context:
Cisco IOS devices such as routers and switches provide different command line privilege levels. When you first connect to a device, you usually land in user EXEC mode, which has limited commands. To perform configuration changes or view detailed information, you must enter privileged EXEC mode. Knowing the command that elevates you from user EXEC to privileged EXEC is a basic but essential Cisco certification topic.

Given Data / Assumptions:

We are at the user EXEC prompt, typically shown as "Router>" or similar.
Privileged EXEC mode is indicated by a prompt like "Router#".
The device is running standard Cisco IOS and is using default command names.

Concept / Approach:
Cisco IOS uses the command "enable" to move from user EXEC mode to privileged EXEC mode. When you type "enable" and press Enter, the router may prompt you for an enable password or enable secret if one is configured. Once authenticated, you gain access to powerful commands, including those that affect the running configuration. Other commands like "configure terminal" are run from privileged EXEC mode to enter global configuration mode, but they do not directly elevate you from user EXEC.

Step-by-Step Solution:
Start at the user EXEC prompt, for example "Switch>". Type the command "enable" and press Enter. If an enable password or enable secret is configured, enter it when prompted. After successful authentication, the prompt changes to "Switch#", indicating that you are in privileged EXEC mode. From privileged EXEC mode, you can then enter configuration modes using commands such as "configure terminal".

Verification / Alternative check:
Cisco command line examples in official documentation and training materials consistently show the sequence: "Router> enable" followed by "Router#" to indicate moving into privileged mode. There is no "su root" or "admin 0" command in standard IOS for this purpose. This consistency across training guides, lab exercises and actual devices confirms that "enable" is the correct and only answer here.

Why Other Options Are Wrong:
Option a ("su root") is a Unix or Linux command used to switch user to the root account; it does not exist in Cisco IOS in this context.
Option b ("admin 0") is not a valid IOS command for changing privilege level.
Option d ("init") might appear in other systems, but is not used to change modes on Cisco IOS devices.
Option e ("configure") or "configure terminal" is used from privileged EXEC mode to enter configuration mode, not from user EXEC to privileged EXEC.

Common Pitfalls:
New network engineers sometimes confuse the roles of "enable" and "configure terminal". Remember that "enable" elevates you into privileged EXEC mode, whereas "configure terminal" changes from privileged EXEC into global configuration mode. Another pitfall is forgetting that an enable password or secret may be required, leading to authentication failures if not known.

Final Answer:
The IOS command used to access high level privileged EXEC commands is "enable".