textbox components error

Don't do it!
Never make your components public - it causes the design of your form to be "locked" - you cannot change the way the form works, because you do not know what the outside world has done with your textbox.

Instead, use a public property:

public AlphabetText
   {
   get { return alphabet_TextBox2.Text; }
   set { alphabet_TextBox2 = value; }
   }

You can then change the way your form works without the outside world being any the wiser, provided that your property returns the same values.