Do coding on onblur event of textbox
for that u will have to take a button and make its visible false on form load event.
i m giving u code use as per your requirement.
protected void Page_Load(object sender, EventArgs e)
{
Button3.Visible = false;
string hanlder1 = ClientScript.GetPostBackEventReference(this.Button3, "");
Textbox2.Attributes.Add("onblur", hanlder1);
}
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Same thing apply for third TextBox and use one more button