Question

What is the relative atomic mass of cadmium?
(A) $112.411amu$
(B) $20.00amu$
(C) $21.00amu$
(D) $20.43amu$

Answer 1

Hint Relative atomic mass is the ratio of the average mass of atoms of a chemical element in a given sample to the atomic mass constant. With the definition of relative atomic mass we can easily find the answer for the above question.

Complete step by step answer
As we know that isotopes are elements whose atomic numbers are the same but have different masses due to the presence of different numbers of neutrons. They are basically the same elements but have different masses.
The relative atomic mass is the average of all the atomic masses of all the different isotopes in a sample. The contribution of each isotope to the average is determined by how much fraction of the sample is naturally found in that isotope form. Relative atomic mass is equal to the average of all the atoms in an element compared to $1/12$ th the mass of a carbon - $12$ atom (carbon- $12$ isotope).
The name cadmium was derived from the Greek word “kadmeia” .It was first found as an impurity in zinc carbonate. It was found in furnace flue dust. This element was discovered and isolated by physician Friedrich Stromeyer in $1871$ . In $1961$ , the chemical measurements showed that cadmium (Cd), the relative atomic mass of $Cd$ was $112.40amu$ . But the mass-spectrometric data recommended the value of average from $112.41$ amu to $112.43$ amu.
Since $2013$ , the relative atomic mass of cadmium is considered to be $112.411$ amu.
Hence, the correct option will be option (A).

Note
The relative atomic mass of cadmium does not show any anomalous value or decay. It did vary before but now it is considered to be one constant value after 2013 and up to till now it is considered as the same.