---

private int secretNumber;
private string[] roman = { "", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX", "X" };

public MainWindow()
{
    InitializeComponent();
    secretNumber = new Random().Next(1, 11);
}

private void Num_Checked(object sender, RoutedEventArgs e)
{
    RadioButton rb = sender as RadioButton;
    if (rb != null && rb.IsChecked == true)
    {
        int chosen = int.Parse(rb.Content.ToString());
        if (chosen == secretNumber)
            MessageBox.Show("Правильно!");
        else
            MessageBox.Show($"Неверно! Загаданное число: {secretNumber}");
        secretNumber = new Random().Next(1, 11);
    }
}