Question

Which of the following are the characteristics of isotopes of an element?
(i) isotopes of an element have the same atomic masses.
(ii) isotopes of an element have the same atomic number.
(iii) isotopes of an element show the same physical properties.
(iv) isotopes of an element show the same chemical properties.

A ) (i), (ii) and (iii)
B ) (ii), (iii) and (iv)
C ) (ii) and (iii)
D ) (ii) and (iv)

Answer 1

Hint: Chemical properties depend on atomic number, number of electrons and the number of valence electrons. Physical properties depend on atomic mass.

Complete answer:
> Isotopes are the different atoms of the same atom. Hence, they have the same atomic number. But isotopes differ in the mass number. For example, three isotopes hydrogen, deuterium and tritium have the same atomic number of 1. But they have different mass numbers. The mass numbers of hydrogen, deuterium and tritium are 1,2 and 3 respectively.
> The atomic number is equal to the number of protons. It is also equal to the number of electrons in a neutral atom. Thus, hydrogen, deuterium and tritium having atomic number of 1 have one electron in their atom. Since the atomic number of different isotopes is the same, the number of electrons for different isotopes is also the same. Hence, isotopes have the same chemical properties.
> Isotopes have different mass numbers. Hence, they have different atomic masses. Hence, isotopes have different physical properties. Mass number is equal to the sum of the number of protons and the number of neutrons.

Hence, the correct option is the option D ) (ii) and (iv).

Note: Usually, it is observed that different isotopes undergo the same reaction at different reaction rates. This is because different isotopes have different activation energy. This is known as kinetic isotopic effect.