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The correct choice is Hydrogen. Hydrogen is the simplest and most abundant element in the universe, consisting of only one proton in its nucleus. The most common isotope of hydrogen, known as protium, has no neutrons, which is why it is the only element that can exist without them.

In contrast, carbon has six protons and typically six neutrons, oxygen has eight protons and eight neutrons, and uranium, a much heavier element, contains a significantly larger number of neutrons as well. Therefore, hydrogen stands out as the element that does not contain any neutrons.