Question

Assertion: All the isotopes of a given element show the same chemical behaviour.
Reason: Isotopes have a different number of neutrons present in the nucleus.
(A)Assertion is true, reason is true and reason is correct explanation for assertion .
(B) Assertion is true, reason is true and reason is not the correct explanation for assertion.
(C) Assertion is true, reason is false.
(D) Assertion is false, reason is true.

Answer 1

An isotope is defined as the compound which has the same atomic number that is the same number of electrons and protons present in the atom. Also the atomic weight of the isotopes is not the same in both of them.

Complete answer: We know that the isotope of an element has the same number of electrons and protons present in the atom but the number of neutrons differs.
The chemical properties of the atom depends on the electronic configuration of the atom. We know that the electronic configuration and the number of atoms remains the same in isotopes . Though the electronic configuration remains the same the chemical properties also remain the same. The mass number in the isotopes is the same so the neutrons are different . Also mass number defines physical properties such as boiling point, melting point and density . But the chemical properties are governed by atomic numbers . The isotopes have similar chemical properties.
So the assertion is correct.
Isotopes have different neutrons and atomic number is constant. So the reason is also correct.
But having the same number of neutrons doesn’t affect the physical properties so it is not the correct explanation of assertion.
Hence assertion and reason both are correct but reason is not a correct explanation of assertion.

Therefore the correct answer is option (B).

Note: Number of protons denote the atomic number. Due to the same number of protons, isotopes have the same atomic number but different mass numbers due to different numbers of neutrons.