How to fix failed to load ad 1 error?

Question

I waant to add ads in my app . Tomorrow I am going to publish this app on playstore. I added but ads nott showing with a error failed to load ad 1 . So please tell me how to fix it ! Thank you in advance.

package com.buckydroid.app.droidcpu;

import android.content.ActivityNotFoundException;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.buckydroid.app.droidcpu.R;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;

/**
 * A fragment that launches other parts of the demo application.
 */
public class PageAbout extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_about, container, false);

     // Gets the ad view defined in layout/ad_fragment.xml with ad unit ID set in
        // values/strings.xml.
        AdView mAdView = (AdView) rootView.findViewById(R.id.ad_view);
        AdRequest adRequest = new AdRequest.Builder().build();
        // Start loading the ad in the background.
        mAdView.loadAd(new AdRequest.Builder().build());

        // Demonstration of a collection-browsing activity.
        rootView.findViewById(R.id.bt_read).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Uri uri = Uri.parse("market://details?id=" + getActivity().getPackageName());
                Intent goToMarket = new Intent(Intent.ACTION_VIEW, uri);
                try {
                  startActivity(goToMarket);
                } catch (ActivityNotFoundException e) {
                    getActivity().startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("http://buckydroid.com" + getActivity().getPackageName())));
                }
            }
        });


        return rootView;
    }
}