multiple checkbox delete in gridview

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C#

i want to delete checkbox on delete button click event..but i cant get id to delete
appropriate checkbox..please help
code is given bellow..

thanx in advance.

SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\rAvIrAj\Downloads\Ravi\Ravi\App_Data\Database.mdf;Integrated Security=True;User Instance=True");
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Grid_Bind();
        }
    }

    public void Grid_Bind()
    {

        SqlCommand cmd = new SqlCommand();

        SqlDataAdapter da = new SqlDataAdapter(); ;

        DataTable dt = new DataTable();
        try
        {
            cn.Open();

            cmd.CommandText = "Select * from Student_Master";

            cmd.Connection = cn;

            cmd.CommandType = CommandType.Text;

            da.SelectCommand = cmd;

            da.Fill(dt);

            gv1.DataSource = dt;

            gv1.DataBind();

            cn.Close();
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }

    }
 
 
 
    protected void chk1_CheckedChanged1(object sender, EventArgs e)
    {
        try
        {
            if (((CheckBox)gv1.HeaderRow.FindControl("chk1")).Checked==true)
            {
                foreach (GridViewRow row in gv1.Rows)
                {
                    ((CheckBox)row.FindControl("chk2")).Checked = true;

                }
            }
            else
            {
                foreach (GridViewRow row in gv1.Rows)
                {
                    ((CheckBox)row.FindControl("chk2")).Checked = false;

                }

            }
        }

        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }
       

    }

    protected void btn_Click(object sender, EventArgs e)
    {
        foreach (GridViewRow row in gv1.Rows)
        {
           
            if (((CheckBox)row.FindControl("chk2")).Checked == true)
            {
                int id =

                SqlCommand cmd = new SqlCommand("delete from Student_Master where id="+id,cn);
                Grid_Bind();
                ll.Text = "successful";
            }
        }
    }