Scandium atoms, reactions

C. All four choices are balanced mathematically. "A" leaves scandium-41 as a decay product, not scandium-45. "B" and "D" require the addition of particles not normally present in the atom. If these reactions do occur, they are not decay reactions because they are not spontaneous. "C" involves the common decay mechanism of beta emission. 

The generation of reactive species by a fast pre-reaction is a well established process in kinetics, particularly in flow systems, although this technique is now being used in molecular beam sources [see (f), below]. As atoms are commonly generated by thermal or microwave dissociation (see above), reactions are mainly used to produce radicals. However, some atoms may be produced by reaction as a more convenient alternative to direct vaporisation or dissociation. Scandium and yttrium atoms have been generated [25] by the reaction... 

Lanthanide elements have atomic numbers ranging from 57 to 71. With the inclusion of scandium (Sc) and yttrium (Y), a total of 17 elements are referred to as the rare earth elements. A mixture of rare earths was discovered in 1794 by J. Gadolin and ytterbium was separated from this mixture in 1878 by Mariganac, while the last rare earth element promethium (Pm) was separated by a nuclear reaction in 1974. Therefore, a period of more than 100 years separates the discovery of all the rare earth elements. In the latter part of the last century scientists started to focus on the applications of rare earth elements. Numerous interesting and important properties were found with respect to their magnetic, optical, and electronic behavior. This is the reason that many countries list all rare earth elements, except promethium (Pm), as strategic materials. Rare earth coordination chemistry, therefore, developed quickly as a result of this increased activity. 

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