Question

consider the nuclear activity ,which of of the following elements is the most unstable one? (A) He² (B) Na¹¹ (C) Xe⁵⁴ (D) Pb⁸² (E) Ra⁸⁸

Answer 1

for a given element if their is neutron and proton balance exists then it is more stable.

that is..

no. of protons = no. of neutrons.

i.e protons and neutrons are in the ratio of 1:1

if this ratio exceeds then nuclear unstability increases

so we have to find out the proton and neutron ratio for the given elements.

A) He

for this atomic no. is 2 and mass no. is 4

no. of neutrons = mass no. - no. of protons ( no. of protons is atomic number)

for He no. of neutrons = 4 - 2 =2

here no. of protons and neutrons are same hence it is nuclear stable element.

B) Na mass no. =23

no. of neutrons = 23 - 11 = 12

here ratio of neutron :proton comes to be 1.09:1 ( ratio determined by dividing no. of neutrons by no. of protons)

hene it is less stable than He.

C) Xe atomic no= 54 mass no. =131.3

no. of neutrons = 131-54= 77

neutron : proton ratio= 1.42 : 1

D) Pb atomic no. 82 mass no.=207.2

no. of neutrons = 207.2-82 =125.2

neutron: proton ratio = 1.52:1

E) Ra atomic number = 88 mass number= 226

no. of neutrons = 226 - 88 = 138

neutron : proton ratio = 1.56 :1

so from the above calculations the stabily order of the elements are as follows

He > Na > Xe > Pb > Ra

hence radium i.e Ra is most unstable element from the given elements.