Question

Which isotope in each pair is more stable? Why?

(a) ${}_{\text{55}}{}^{\text{140}}\text{Cs}$or ${}_{\text{55}}{}^{\text{133}}\text{Cs}$ (b)${}_{\text{35}}{}^{\text{79}}\text{Br}$or ${}_{\text{35}}{}^{\text{78}}\text{Br}$

(c) ${}_{\text{12}}{}^{\text{28}}\text{Mg}$or ${}_{\text{12}}{}^{\text{24}}\text{Mg}$ (d) ${}_{\text{7}}{}^{\text{14}}\text{N}$or${}_{\text{7}}{}^{\text{18}}\text{N}$

Short answer

a) ${}_{\text{55}}{}^{\text{133}}\text{Cs}$is more stable isotope

b) ${}_{\text{35}}{}^{\text{79}}\text{Br}$is more stable isotope

c) ${}_{\text{12}}{}^{\text{24}}\text{Mg}$is more stable isotope

d) ${}_{\text{7}}{}^{\text{14}}\text{N}$is more stable isotope

Step-by-step solution

Definition of Isotope

Isotopes are chemical elements that have the same number of protons and electrons but differ in the number of neutrons they have.

Determining more stable isotope

a)${}_{\text{55}}{}^{\text{133}}\text{Cs}$

In comparison to${}_{\text{55}}{}^{\text{133}}\text{Cs}$ , the N/Z ratio ofdata-custom-editor="chemistry" ${}_{\text{55}}{}^{\text{140}}\text{Cs}$ is higher.

Determining more stable isotope

b)${}_{\text{35}}{}^{\text{79}}\text{Br}$

In comparison to ${}_{\text{35}}{}^{\text{79}}\text{Br}$, this isotope has an even number of neutrons.

Determining more stable isotope

c)${}_{\text{12}}{}^{\text{24}}\text{Mg}$

Its N/Z ratio is equal to one.

Determining more stable isotope

d)${}_{\text{7}}{}^{\text{14}}\text{N}$

Its N/Z ratio is equal to one.