Astatine (At) is a radioactive element. Study the graph given below showing the number of protons vs the number of neutrons of radioactive nuclei.

(a) Identify the mass number of the nucleus Astatine (At).

(b) Which line on the graph (l, m, n, or q) will never pass through the position of the daughter nuclei, regardless of any number of α, β, or γ emissions?

(c) Give a reason for your choice in (b).

(a) From the graph,

Number of protons in Astatine = 85

Number of neutrons in Astatine = 126

Then,

Mass number of Astatine = Number of protons + Number of neutrons = 85 + 126 = 211

(b) The line m on the graph will never pass through the position of the daughter nuclei, regardless of any number of α, β, or γ emissions.

(c) As line m represents a daughter nucleus which has one excess neutron than Astatine and from α, β, or γ emissions, none has ability to increase the neutron number of Astatine and produce a daughter nucleus with one excess neutron so line m can not pass through any daughter nucleus of Astatine.