Q.Which of the following statements about hydrogen is incorrect? (NEET - 2016)

Hydrogen has three isotopes: protium $(_1^1H)$, deuterium $(_1^2H$ or $D)$, and tritium $(_1^3H$ or $T)$, all having the same number of protons and electrons (1) but differing in the number of neutrons — 0, 1 and 2 respectively. This gives them a mass ratio of approximately $1:2:3$. Protium is the most abundant, ordinary form found in nearly all hydrogen compounds. Deuterium occurs naturally in trace amounts (about 1 part in 6500 of protium) and is the isotope present in heavy water, $D_2O$. Tritium is radioactive, emitting low-energy beta particles, and occurs only in minute natural quantities, being formed continuously in the upper atmosphere by cosmic-ray interactions; it is also produced artificially in nuclear reactors. Because chemical behaviour is governed by the number and arrangement of electrons, all three isotopes react chemically in essentially the same way, but their differing masses cause measurable differences in physical properties and reaction rates — the kinetic isotope effect — and in the strength and vibrational frequency of the bonds they form.

Isotopes of hydrogen — protium, deuterium and tritium — form a core topic of the CBSE Class 11 Chemistry NCERT Hydrogen chapter, searched as "isotopes of hydrogen class 11 chemistry" or "protium deuterium tritium differences important questions". Their mass ratio and the kinetic isotope effect are frequently tested facts in board exams and NEET.