Question

deuterium is an isotope of hydrogen. it has a mass number of two. which describes a deuterium atom?
o a. a nucleus of one proton and one neutron, which is orbited by one electron
o b. a nucleus of one proton, which is orbited by one neutron and one electron
o c. a nucleus of one neutron, which is orbited by one electron
o d. a nucleus of two neutrons which is orbited by two electrons

Explanation:

To determine the correct description of a deuterium atom (an isotope of hydrogen with mass number 2), we recall the structure of hydrogen isotopes. Hydrogen has 1 proton. For deuterium, the mass number (protons + neutrons) is 2, so neutrons = 2 - 1 = 1. A neutral atom has equal protons and electrons, so 1 electron orbits the nucleus.

• Option A: Nucleus has 1 proton and 1 neutron (correct for mass number 2), and 1 electron orbiting. This matches.
• Option B: Says the nucleus has 1 proton, orbited by 1 neutron (neutrons are in the nucleus, not orbiting) and 1 electron. Incorrect.
• Option C: Nucleus has 1 neutron (but hydrogen must have 1 proton, so nucleus should have 1 proton + 1 neutron, not just 1 neutron). Incorrect.
• Option D: Nucleus with 2 neutrons (mass number would be 1 + 2 = 3, for tritium, not deuterium) and 2 electrons (incorrect, should be 1 electron). Incorrect.

Answer:

A. a nucleus of one proton and one neutron, which is orbited by one electron