Elementary Particle With No Charge, Proved in 1956
Puzzle 9 of The 1950s Hard Pack
Question is: Elementary Particle With No Charge, Proved in 1956
and the answer is: NEUTRINO
Word Meaning:
NEUTRINO — An elementary particle that is classified as a lepton, and has an extremely small but nonzero mass and no electric charge. It interacts with the surroundings only via the weak force or gravitation, making it very difficult to detect.
Definitions from Wiktionary.