Android Devices How to enable and disable the silent mode?

You can use the AudioManager to enable and disable silent mode. 

mAudio = (AudioManager) getSystemService(Activity.AUDIO_SERVICE);

mAudio.setRingerMode(AudioManager.RINGER_MODE_SILENT);

// or...

mAudio.setRingerMode(AudioManager.RINGER_MODE_NORMAL);

Android Wifi How to enable and disable Wifi?

          The WifiManager can be used to enable and disable wifi. Where 'enabled' is a boolean. 

       WifiManager wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);

       wifi.setWifiEnabled(enabled);