ODP.NET

public partial class Form1 : Form
{
    string connectionstring = @"DATA    SOURCE=server/orcl;TNS_ADMIN=C:\\Users\\hp\\Oracle\\network\\admin;User Id=user id;Password=xxxxx;Pooling=True;Min Pool Size=1;Max Pool Size=100;Incr Pool Size=5;Decr Pool Size=1;Connection Lifetime=0;Connection Timeout=15;Validate Connection=false;Self Tuning=True";

    public Form1()
    {
        InitializeComponent();
    }

    private void btnTestConn_Click(object sender, EventArgs e)
    {
        // OracleConnection conn = new OracleConnection();
        try
        {
            using (OracleConnection conn = new OracleConnection(connectionstring))
            {
                MessageBox.Show(conn.State.ToString());
                conn.Open();

                MessageBox.Show("Database is opened....");

                conn.Close();

                MessageBox.Show("Database is closed....");
            }
        }
        catch (OracleException ex) // catches only Oracle errors
        {
            switch (ex.Number)
            {
                case 1:
                    MessageBox.Show("Error attempting to insert duplicate data.");
                    break;

                case 12545:
                    MessageBox.Show("The database is unavailable.");
                    break;

                default:
                    MessageBox.Show("Database error: " + ex.Number.ToString());
                    break;
            }
        }
        catch (Exception ex) // catches any error
        {
            MessageBox.Show(ex.Message.ToString());
        }
    }
}