Error in mainactivity java file before that these are separate activities but when i connect two activities i got error

Question

1.Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

2.First I added my two activities then I got this error

Below is XML code:- Exact what line i got this error please give the solution with code.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity2">

        <TextView
            android:id="@+id/textview"
            android:layout_width="346dp"
            android:layout_height="40dp"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:gravity="center"
            android:text="Text to Speech"
            android:textColor="#F32269"
            android:textSize="28dp"
            android:textStyle="bold" />


        <SeekBar
            android:id="@+id/seek_bar_speed"
            android:layout_width="389dp"
            android:layout_height="28dp"
            android:layout_below="@id/textview"
            android:layout_alignParentStart="true"
            android:layout_alignParentEnd="true"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="31dp"
            android:layout_marginEnd="4dp"
            android:progress="50" />

        <TextView
            android:layout_width="match_parent"
            android:layout_height="28dp"
            android:layout_alignBottom="@id/textview"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:layout_marginStart="1dp"
            android:layout_marginTop="41dp"
            android:layout_marginBottom="-29dp"
            android:gravity="center"
            android:text="Speed"
            android:textColor="@color/black"
            android:textSize="20dp" />

        <ScrollView
            android:layout_width="wrap_content"
            android:layout_height="363dp"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"
            android:layout_alignParentEnd="true"
            android:layout_centerInParent="true"
            android:layout_marginStart="0dp"
            android:layout_marginTop="100dp"
            android:layout_marginEnd="2dp">

            <EditText
                android:id="@+id/editText"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:hint="       Enter  Text             "
                android:textColor="#000000"
                android:textColorHint="#51FA2B"
                android:textSize="20dp"
                tools:layout_conversion_absoluteHeight="45dp"
                tools:layout_conversion_absoluteWidth="89dp"
                tools:layout_editor_absoluteX="12dp"
                tools:layout_editor_absoluteY="179dp" />

        </ScrollView>

    <Button
        android:id="@+id/button"
        android:layout_width="418dp"
        android:layout_height="71dp"
        android:layout_alignParentStart="true"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        android:layout_marginStart="0dp"
        android:layout_marginTop="74dp"
        android:layout_marginEnd="-7dp"
        android:layout_marginBottom="134dp"
        android:text="Text to speech"
        android:textSize="18dp"
        android:textStyle="bold"/>




</RelativeLayout>

import android.os.Bundle;
import android.speech.tts.TextToSpeech;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import java.util.Locale;
import android.widget.Toast;
import android.content.Intent;

import androidx.appcompat.app.AppCompatActivity;
import android.widget.TextView;
import android.widget.SeekBar;

public class MainActivity2 extends AppCompatActivity {
    TextView textView;
    private SeekBar mseekbar;
    TextToSpeech t1;
    EditText ed1;
    Button b1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ed1 = findViewById(R.id.editText);
        b1 = findViewById(R.id.button);
        textView = findViewById(R.id.text);
        mseekbar = findViewById(R.id.seek_bar_speed);

        t1 = new TextToSpeech(getApplicationContext(), new TextToSpeech.OnInitListener() {
            @Override
            public void onInit(int status) {
                if (status != TextToSpeech.ERROR) {
                    t1.setLanguage(Locale.US);
                }
            }
        });

        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String toSpeak = ed1.getText().toString();
                float speed = (float) mseekbar.getProgress() / 50;


                t1.setSpeechRate(speed);
                Toast.makeText(MainActivity2.this.getApplicationContext(), toSpeak, Toast.LENGTH_SHORT).show();
                t1.speak(toSpeak, TextToSpeech.QUEUE_FLUSH, null);
            }
        });
    }

    public void onPause() {
        if (t1 != null) {
            t1.stop();
        }
        super.onPause();
    }

}```