Which of the following actions is illegal while driving?

Driving with a blood alcohol concentration (BAC) above the legal limit is illegal because it compromises the driver's ability to operate a vehicle safely. Excessive alcohol consumption impairs judgment, reaction time, coordination, and overall cognitive function, significantly increasing the risk of accidents. Laws are established to maintain public safety, and driving under the influence of alcohol can lead to severe legal consequences, including fines, license suspension, and even imprisonment.

In contrast, using hands-free devices, adjusting the seat for comfort, and listening to the radio are generally considered legal actions while driving, provided they do not distract the driver to a dangerous extent. These activities are seen as permissible unless they lead to impaired vehicle control or situational awareness.