Explain qualitatively yet with supporting relations the following observations about Bohr orbits in hydrogen-like atoms:
(a) The radius of an orbit increases with the square of the principal quantum number but decreases with increasing nuclear charge.
(b) The speed of the electron decreases as n increases, yet increases if the same orbit number is considered for a higher-Z ion.
(c) The total energy becomes less negative (i.e., approaches zero) as n increases. What does this imply about the stability of higher orbits?
(d) Why is the concept of stationary states essential to avoid continuous radiation according to classical electrodynamics?