Q. Consider the following milestones in the history of Physics:
  1. Discovery of X-rays by Roentgen
  2. Publication of Newton's Principia Mathematica
  3. Discovery of electron by J.J. Thomson
  4. Formulation of Maxwell's equations
Which of the following gives the correct chronological order of these events?

Answer: 2 → 4 → 1 → 3
Notes: Newton's Principia Mathematica was published in 1687. Maxwell's equations were formulated in the 1860s. Wilhelm Roentgen discovered X-rays in 1895, and J.J. Thomson discovered the electron in 1897. Thus, the correct chronological sequence is 2 → 4 → 1 → 3.