Final answer:
Hydrogen and carbon each have two stable isotopes. Uranium, despite having six isotopes, has no stable isotopes as all are radioactive. Oxygen has three stable isotopes, with oxygen-16 being the most common.
Step-by-step explanation:
The number of stable isotopes an element has can vary significantly. In the case of hydrogen, carbon, uranium, and oxygen, the stable isotopes are identified by the total count of protons and neutrons in the nucleus.
Hydrogen has two stable isotopes: hydrogen-1 (protium, 1H), with no neutrons, and hydrogen-2 (deuterium, 2H or D), with one neutron. The third isotope, hydrogen-3 (tritium, 3H or T), is radioactive and not considered stable. Therefore, hydrogen has two stable isotopes.
Carbon has two natural isotopes that are stable: carbon-12 (12C), with six neutrons and carbon-13 (13C), with seven neutrons. Carbon-14 (14C), with eight neutrons, is radioactive and not stable. Thus, carbon has two stable isotopes.
Uranium typically has six isotopes, but none of them are stable; they are all radioactive to different extents. Nevertheless, the most common isotopes found in nature are uranium-238 and uranium-235, of which uranium-238 is the most abundant.
Oxygen has three stable isotopes: oxygen-16 (16O), with eight neutrons, oxygen-17 (17O), with nine neutrons, and oxygen-18 (18O), with ten neutrons. The most abundant is oxygen-16.