Answer:
21H deuterium (D), 31H is tritium (T), 11H is hydrogen
Step-by-step explanation:
11H: it has the greatest abundance, it has only one proton (it does not have neutrons).
21H (D): it has a proton and a neutron in its nucleus.
31H (T): it has a proton and two neutrons in its nucleus.
Remember that isotopes have the same atomic number, but a different mass number (elements in the number of neutrons differed).