Question

Isotope ?-1 has an atomic mass of 1.

99.985% of all atoms of element ? are of this
form.
Isotope ?-2 has an atomic mass of 2
0.015% of all atoms of element ? are of this form.

Answer 1

Answer: Isotope-1: Hydrogen (H)

Isotope-2: Deuterium (H)

Explanation: The periodic table shows that the smallest element in hydrogen (H), at an average atomic weight of 1.008. Hydrogen-1 has one proton, one electron, and no neutrons, which adds to 1 AMU. Hyrogen-2 is an isotope of hydrogen that contains 1 neutron in addition to the proton, bringing the mass to 2 AMU. It is only at 0.0156% abundance on Earth and is given the name Deuterium, sometimes refered to as "heavy water" when incorporated into a water molecule. A third isotope has 2 neutrons, and is called Tritium.