The only element in the universe with a single proton in the nucleus is hydrogen (H), distinguishing it from all other elements.
Scientists use the number of protons in an atom's nucleus to distinguish between different elements. The element that has only one proton in its nucleus is hydrogen (H). No other element in the universe shares this singular characteristic. Isotopes of hydrogen, such as deuterium (2H) and tritium (3H), share the common feature of having one proton but differ in the number of neutrons. The most abundant isotope of hydrogen, protium, has exactly one proton and no neutrons in its nucleus, making it the simplest atom.
An atom with two protons is always identified as helium (He), three protons as lithium (Li), and the pattern continues with each element being defined by its unique number of protons, such as six for carbon (C) and eight for oxygen (O). Therefore, the answer to the question is A) Hydrogen (H), which is the only element with a single proton in its nucleus.