Asked by qp
The atomic symbol Superscript 40 subscript 19 upper K. represents potassium-40 (K-40), a radioactive isotope that has 19 protons and 21 neutrons. Which atomic symbol could represent an isotope that results from the decay of K-40?
Superscript 40 subscript 18 upper A r.
Superscript 40 subscript 18 upper K
Superscript 42 subscript 20 upper C a
Superscript 42 subscript 20 upper K.
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Superscript 40 subscript 18 Ar.
Reason: K-40 (Z=19, A=40) can decay to Ar-40 (Z decreases to 18 by electron capture) or to Ca-40 (Z increases to 20 by β− decay). Of the choices given, only 40/18 Ar is a correct decay product. The others either have the wrong mass number or an inconsistent element symbol/atomic number.
Reason: K-40 (Z=19, A=40) can decay to Ar-40 (Z decreases to 18 by electron capture) or to Ca-40 (Z increases to 20 by β− decay). Of the choices given, only 40/18 Ar is a correct decay product. The others either have the wrong mass number or an inconsistent element symbol/atomic number.
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