Nguyen Nhat Minh took gold at the competition, held July 4 to 12 in Bucaramanga, Colombia, with a perfect 30 out of 30 on the theoretical section.
The only other contestant to match him at the same exam was Vu Nguyen Nguyen, an 11th grader from Hanoi-Amsterdam High School for the Gifted.
Their scores carried Vietnam's five-member team to a top-seven finish among the 85 competing countries and territories, the best result in the country's IPhO history.
The four golds and one silver equaled Vietnam's 2017 haul, but no contestant that year scored perfect on theory.
Perfect theory scores are extremely rare, even for powerhouse teams like China's, said Assoc. Prof. Nguyen Cong Toan, a vice principal at Minh's school who has worked with Olympiad students for 15 years.
