Identify the pair A. 126 X, 136 y
B. 3517X, 3717Y
C. 146 X, 147 Y
D. 84X, 85Y
Isotopes are species of same elements having different mass number (proton+neutron) number, they have the same atomic number or proton numbers but differ in numbers of neutrons.
Therefore, the entities (iii)146 X, 147 Y and (iv)84X, 85Y are not at all isotopes as they have atomic numbers 6 and 7, 4 and 5 respectively.
Other 2 options (i) 126 X, 136 y (ii) 3517X, 3717Y are definitely isotopes.
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