Question

Which of the following atomic and physical properties of hydrogen is false?
A.Hydrogen > Deuterium > Tritium: (melting point/ K)
B.Hydrogen < Deuterium < Tritium: (boiling point/ K)
C.Hydrogen < Deuterium < Tritium: (density/ $$\text{g}{\text{L}}^{\text{ - 1}}$$ )
D.Hydrogen > Deuterium > Tritium: (% relative abundance)

Answer 1

Hint:(1) In chemistry, the term isotope is used to define the variants of an atom of a chemical element which have the same atomic number but different mass number. In other words, isotopes of an element have the same number of protons but different number of neutrons.
(2) The element hydrogen has three naturally occurring isotopes which are protium, deuterium and tritium. Protium is simply called hydrogen.

Complete step by step answer:
Let us discuss the properties of the three isotopes of hydrogen.
-Protium is the most common isotope of hydrogen and it has an abundance of about more than 99.98%. The nucleus of the protium isotope consists of only one proton and no neutrons. That is why it is given the rarely used name ‘protium’ and the atomic symbol is ${}^{\text{1}}\text{H}$ . The mass of this isotope is 1.007825 amu. Monoatomic hydrogen is rare. This isotope is usually found in the form of diatomic hydrogen gas (${\text{H}}_{\text{2}}$) or in combination with other elements. The $\text{H - H}$ bond is very strong and has a bond dissociation energy of about 435.88 $\text{kJmo}{\text{l}}^{\text{ - 1}}$ .
-Deuterium is the other most stable isotope of hydrogen and it accounts for about 0.02 % of all hydrogen occurring naturally in oceans. The nucleus of the deuterium isotope consists of only one proton and one neutron and so its symbol is ${}^2\text{H}$. Because of the extra neutron, its mass is twice the mass of protium. Its bond dissociation energy is about 443.4 $\text{kJmo}{\text{l}}^{\text{ - 1}}$.
-The third isotope of hydrogen is tritium and it is extremely rare on earth. It has one proton and two neutrons and hence the symbol ${}^3\text{H}$ . Because of the extra two neutrons, its mass is thrice the mass of protium. Its bond dissociation energy is about 446.9 $\text{kJmo}{\text{l}}^{\text{ - 1}}$.
-Since melting and boiling points increase with increase in mass, the melting and boiling point order is: hydrogen < deuterium < tritium. So, the option A is wrong and B is correct.
-Since density is also directly proportional to mass, the density order will also be hydrogen < deuterium < tritium. So, the option C is correct.
-Lastly, the abundance of hydrogen protium is more than that of deuterium and tritium is rare. So, the order of abundance: hydrogen > deuterium > tritium. So, the option D is correct.

Hence, option A is false.

Note:
Some other properties of these isotopes are: Deuterium is not radioactive and water that contains deuterium instead of hydrogen is called heavy water. Deuterium is also used in ${}^{\text{1}}\text{H}$ NMR spectroscopy. Tritium is radioactive and it keeps decaying into helium – 3 via beta decay.