Final answer:
When Edmund Hillary and Tenzing Norgay reached the summit of Mount Everest on May 29, 1953, the coronation of Queen Elizabeth II occurred concurrently in London.
Step-by-step explanation:
At the same time as Edmund Hillary and Tenzing Norgay successfully summited Mount Everest on May 29, 1953, another important historic event took place. While option a) An earthquake struck the Everest region is related to a 2015 tragedy and not the 1953 expedition, and option c) The first ascent of K2 took place in 1954, a year after the Everest expedition.
Option b) Another expedition reached the summit is also incorrect because Hillary and Norgay were the first to reach the summit of Everest. The correct answer is d) The coronation of Queen Elizabeth II, which happened in London on the same day that Hillary and Norgay reached the summit of Everest.