Question

(a) An isotope with 20 protons or less will be stable if: (Select all that apply.)

1. it has more protons than neutrons

2. it has more protons than electrons

3.it has more electrons than protons

4.it has more electrons than neutrons

5.it has the same number of protons and neutrons

6.it has the same number of protons and electrons

(b) An isotope with more than 83 protons is: (Select all that apply.)

1.stable

2.unstable or radioactive

3.will be stable or unstable, depending on its proton to neutron ratio

4.will be stable or unstable, depending on its electron to neutron ratio

5.will be stable or unstable, depending on its proton to electron ratio

Answer 1

Since For a neutral atom
the number of protons = number of electrons = Atomic number Hence for the question first the option correct are options 5 and 6. The number of protons, number of electrons and number of protons will be same
The general criteria for stability for the atomic number Z less than or equal to 20 is that when ratio of neutron to protons is close to 1 and the nucleous contains the protons and neutrons in even quantity then it is mos likely to be stable

When the neutron to proton ratio ie n/p is more than or equal to 1.29 then the unstability is there. The atomic number more than or equal to 82 does not have unstable nucleous and also they are radioactive. An element with atomic number Z> 82 does not observed to have stable nucleous. The neutrons to proton ratio is also found to be high. For example Uranium has atomic number 92 and mass number 238. Number of protons = number of electrons= atomic number =92
Number of neutrons = Mass number - number of protons = 238-92 =146
the neutron to proton ratio (n/p) = 146/92 = 1.587
Hence Uranium is unstable nucleous and radioactive
For this case option 2, 3 and 4 are correct