Question

Which of the following is/are not radioactive element(s)?
A.Sulphur
B.Tellurium
C.Selenium
D.Polonium

Answer 1

Mostly the radioactive elements are the elements having higher atomic mass. Usually (for hit and trial) the radioactive element starts from atomic number $84$ in periodic table.

Complete step by step answer:
Sulphur is a group $16$ element with atomic number 16 and atomic mass $32amu$. Sulphur atoms are found in the form of sulphur molecules with a formula $\mathop S\nolimits_8$.So it is a non-radioactive element.
Tellurium is a group $16$ element with atomic number $54$ and atomic mass $127$. It is found out in the form of elementals crystals. So it is a non-radioactive element.
Selenium is a group $16$ element with atomic number $32$ and atomic mass $78.96u$. It is found in the form of an elemental state having allotropes with colour black, red and grey. Thus it is also a non-radioactive element.
Polonium is a group $16$ element with atomic number $84$ and atomic mass $204$. It is a highly radioactive element with no stable isotope.
So the answer is Sulphur, Tellurium and Selenium.

Additional Information: - All the elements after atomic number $83$ to atomic number $118$ i.e. from polonium to oganesson are radioactive. All actinides and period $7$ elements come into this category.

Note: There are some exceptions that are also there which need to be remembered. Elements like technetium ($\mathop T\nolimits_C$ ) with atomic number $43$ of period $5$ and promethium(Pm) with atomic number $61$ of lanthanides are exceptionally radioactive