Final answer:
The atomic structure of an atom with 2 protons and 4 neutrons corresponds to an isotope of helium, specifically helium-6, which has a mass number of 6 due to the extra neutrons.
Step-by-step explanation:
The atomic structure of an atom with 2 protons and 4 neutrons is best described by option 1: 2 protons and 4 neutrons. Protons are positively charged, and neutrons have no charge, so together they comprise the atom's nucleus. The atomic number, which is the number of protons, is essential in defining the element, and in this case, the element is helium. Typically, helium has 2 neutrons, but with 4 neutrons, it becomes an isotope of helium known as helium-6. This isotope has a greater mass number than the common helium-4 isotope, due to the extra neutrons. However, the number of protons remains the same, preserving the chemical identity of the element as helium.
Isotopes
are variations of elements differing in the number of neutrons while having the same atomic number. The standard helium atom has a mass number of 4, indicating it usually has two neutrons, but helium-6 is an example of one of helium's rarer isotopes with additional neutrons.