Question

The isotopes of hydrogen have different physical properties due to the difference in the mass. They have almost same chemical properties with a difference in their rates of reactions which is mainly due to:
A. their different enthalpy of bond dissociation
B. different electronic configurations
C. different atomic mass
D. different physical properties

Answer 1

Atoms of an element that have the same number of protons and electrons but have different number of neutrons are called isotopes. Stable isotopes are nuclei that do not appear to decay to other isotopes. Radioactive isotopes are nuclei that spontaneously disintegrate over time to form other isotopes.

Complete step by step solution:
Atoms contain a central nucleus having electrons around it in circular orbits. Atomic number, ${\text{Z}}$ is the number of protons in an atom. Mass number, ${\text{A}}$ is the number of protons and neutrons in an atom. The number of protons is equal to the number of electrons.
The chemical symbol of an element can be represented by ${}_{\text{Z}}^{\text{A}}{\text{X}}$. Isotopes have the same ${\text{Z}}$ but different ${\text{A}}$. Also they have the same chemical properties but slightly different physical properties. They are still the same element, but they have different weights because they have different numbers of neutrons.
Some of the elements having isotopes are hydrogen, carbon, iodine, chromium, helium, nitrogen etc. The first element in the periodic table is hydrogen. It has atomic number one. Hydrogen has three isotopes-Protium ${}_1^1{\text{H}}$, Deuterium ${}_1^2{\text{H}}$ or ${\text{D}}$ and Tritium ${}_1^3{\text{H}}$ or ${\text{T}}$. In protium, there is only one proton and no neutrons. In deuterium, there are one proton and one neutron. In tritium, there are two neutrons and one proton. It is radioactive and emits low energy particles. Their rates of reactions are different because they have different bond dissociation enthalpies.

Hence the correct option is A.

Note: Isotopes have different physical properties because they have very huge variation in their mass. Due to the mass difference, it is difficult to break the bond. Thus the energy will be different for each isotope.