This article explains how to mute the sound on an iPad and what happened to the tablet's mute button.
How to Turn Silent Mode On or Off on Your iPad (Tutorial)
The iPad can be muted in several ways
The easiest way to mute an iPad is to use the volume buttons. As with all standard volume buttons, you simply press and hold Volume Down until the sound goes off to mute your iPad. Some models also have a hardware mute button.
Another way to mute an iPad is to use the options in the Settings app. These settings don’t apply to every sound. They control ringtones and alerts and alarms, but not audio from a streaming video, for example. Follow these steps to adjust these settings: