Answer:
the pair of isotopes are b and e
the element with mass no of 19 is C
the element with atomic no 7is D
Step-by-step explanation:
B and E are isotopes bcos they have the same atomic no, i.e no of protons. They bother have atomic no of 17 BUT have different mass no i.e sum of neutrons and protons.
(b)C is correct because the sum of the protons and neutrons is 19
(c) D because it has 7 protons