Answer:
D.The radioactive decay of an atom
Explanation:
Newtonian physics is related to particle physics in which we deal with the properties exhibit by particles like
1). Momentum conservation
2). Particle collision theory
3). Particle dynamics
So as per all above theory we can use momentum conservation and energy conservation to find the different phenomenon.
But we could not explain the decay of radioactive atom using all above theory as it is due to unstability of nucleus and it is only explained by Einstein theory of relativity.

So here correct answer would be
D.The radioactive decay of an atom