Question

Choose the element which is not radioactive.
A. $Cm$
B. $No$
C. $Mo$
D. $Md$

Answer 1

Hint: Radioactivity is a property of radioactive substances. Radioactive substance undergoes several modes of decay to make the radioactive nucleus stable. The radioactive nuclides undergo decay to give alpha, beta, gamma, X-rays. All this rays have different energy, different characteristics.

Complete Step by Step Solution:
All the actinides are radioactive. Actinides are highly unstable and undergo several modes of decay to stable the element. Here $Cm,Md,No$ are actinides. Thus they are radioactive.
$Mo$ is a $4d$ transition element. It is not radioactive and highly stable.
Thus the correct option is C.

Additional information: Actinides are $5f$ block elements. They show different magnetic and spectral properties. The absorption band of actinides is weak due to orbitally forbidden $5f\to 5f$ transition. Again due to the crystal field effect they show a higher intense band than lanthanides. Actinides show several oxidation states up to $7$ . They can form complexes of higher coordination number like lanthanides. Transition elements have electrons in $d$ orbital. Transition elements show high crystal field effects due to interaction with ligands. They give a highly intense absorption band due to orbitally allowed transitions.

Note: All the actinides are highly radioactive but the highest radioactivity is shown by uranium. These elements undergo decay to form stable nuclide and thus produce alpha particle or ray, beta particle and gamma ray.