Occurrence and Isotopes of Hydrogen — Prelims Questions

Which of the following statements about the isotopes of hydrogen is INCORRECT?

Which of the following is NOT a significant terrestrial source of hydrogen?

What is the number of neutrons in a tritium atom?

Which of the following properties is expected to be higher for $D_2O$ compared to $H_2O$?

The most abundant element in the universe is:

Which isotope of hydrogen is used as a moderator in nuclear reactors?