My Mac book air is not detecting wifi for past 2 days.

If your Macbook Air is not detecting any Wi-Fi networks, here are some steps you can try:

1. Check your Wi-Fi settings: Make sure your Wi-Fi is turned on and your Macbook is not set to "disconnect from this network when it is not in use."
2. Restart your Macbook: Sometimes a simple restart can fix the issue.
3. Reset the SMC: If restarting your Macbook didn't help, you can try resetting the SMC (System Management Controller). To do this, shut down your Macbook, then press and hold the left Shift + Control + Option keys, along with the power button, for 10 seconds. Release all the keys and turn your Macbook back on.
4. Remove and Re-add Wi-Fi network: Remove the Wi-Fi network from your list of known networks and then add it back again.
5. Create a new network location: Sometimes creating a new network location can fix Wi-Fi issues. To do this, go to System Preferences > Network, click the "+" button, select Wi-Fi and give your new network location a name.
6. Try Safe Mode: Starting your Macbook in Safe Mode can help diagnose and fix Wi-Fi issues. To do this, restart your Macbook and hold down the Shift key until the Apple logo appears.