One atom of iron contains 26 protons, 30 neutrons, and 26 electrons. which of the following would be possible for another atom of iron?
26 protons, 28 neutrons, 26 electrons
27 protons, 30 neutrons, 26 electrons
25 protons, 30 neutrons, 26 electrons
25 protons, 30 neutrons, 27 electrons

The atom with 26 protons, 28 neutrons, 26 electrons is another iron atom.

Explanation:

An iron atom has 26 protons. All iron atoms (and isotopes) have the same number of protons but different number of neutrons.

The number of protons gives us an idea of what atom it is.

An atom wih 25 protons is Manganese ( or an isotope of manganese)

An atom with 26 protons is Iron (or an isotope of iron)

An atom with 27 protons is Cobalt (or an isotope of cobalt)

An atom with 26 protons (and electrons) and 28 neutrons is 54Fe. It's one of the four stable isotopes of Iron.

There is only 1 stable cobalt isotope. This has 27 protons and 32 neutrons.

There is only 1 stable Manganese isotope. This has 25 protons and 30 neutrons.

The atom with 26 protons, 28 neutrons, 26 electrons is another iron atom.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.