Question

I need to pass a string value from Form1:

public void button1_Click(object sender, EventArgs e)
{
    string DepartmentName = "IT";
    Form2 frm2 = new Form2();

    Frm2.Show();
    this.Hide();
}

into the Form2 Load event. For example:

private void Form2_Load(object sender, EventArgs e)
{
    MessageBox.Show(DepartmentName);
    // or 
    // string sql1 = "select Service_Name from Service, " +
    //    "EmployeeService where E_Dep = '" + DepartmentName + "' " +
    //    "and s_ID = Service_ID";
}

Answer 1

Just create a property on the Form2 class and set it before you show Form2.

public class Form2
{
   ...
   public string MyProperty { get; set; }

   private void Form2_Load(object sender, EventArgs e)
   {
       MessageBox.Show(this.MyProperty);
   }
}

From Form1:

public void button1_Click(object sender, EventArgs e)
{
    string departmentName = "IT";
    Form2 frm2 = new Form2();
    frm2.MyProperty = departmentName;
    frm2.Show();
    this.Hide();
}