The atomic numbers and mass numbers of the nuclei of hydrogen, deuterium and tritium, respectively are in the ratio
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 1:1:1 and 1:2:3
Hydrogen, deuterium and tritium are isotopes of hydrogen: they have the same number of protons (the same atomic number) but different numbers of neutrons, so their mass numbers differ.
Hydrogen: 1 proton, so \( Z = 1,\ A = 1 \)
Deuterium: 1 proton + 1 neutron, so \( Z = 1,\ A = 2 \)
Tritium: 1 proton + 2 neutrons, so \( Z = 1,\ A = 3 \)
So the atomic numbers are in the ratio 1 : 1 : 1 and the mass numbers in the ratio 1 : 2 : 3.
NCERT (2026-27):
Discovery of Neutron – “Since the nuclei of deuterium and tritium are isotopes of hydrogen, they must contain only one proton each. But the masses of the nuclei of hydrogen, deuterium and tritium are in the ratio of 1:2:3.”