question_answer

Which of the following triads represents isotones? (a) \[_{6}^{12}C,_{6}^{13}C,_{6}^{14}C\]                              (b) \[_{18}^{40}Ar,_{20}^{42}Ca,_{21}^{43}Sc\] (c) \[_{18}^{40}Ar,_{20}^{40}Ca,_{21}^{41}Sc\]  (d) \[_{7}^{14}N,_{8}^{60}O,_{9}^{18}F\]

Answer:

Isotones contain same number of neutrons. Let?s check no. of neutrons in each set.

a)	Atom	No. of neutrons
	\[_{6}{{C}^{12}}\]	\[12-6=6\]
	\[_{6}{{C}^{13}}\]	\[13-6=7\]
	\[_{6}{{C}^{14}}\]	\[14-6=8\]
b)	Atom	No. of neutrons
	\[_{18}A{{r}^{40}}\]	\[40-18=22\]
	\[_{20}C{{a}^{42}}\]	\[42-20=22\]
	\[_{21}S{{c}^{43}}\]	\[43-21=22\]
c)	Atom	No. of neutrons
	\[_{18}A{{r}^{40}}\]	\[40-18=22\]
	\[_{20}C{{a}^{40}}\]	\[40-20=20\]
	\[_{21}S{{c}^{41}}\]	\[41-21=20\]
d)	Atom	No. of neutrons
	\[_{7}{{N}^{14}}\]	\[14-7=7\]
	\[_{8}{{O}^{16}}\]	\[16-8=8\]
	\[_{9}{{F}^{18}}\]	\[18-9=9\]

From the above charts it is clear that \[_{18}A{{r}^{40}}\] \[_{20}C{{a}^{42}}\] and \[_{21}S{{c}^{43}}\] are isotones.