What is an isotope? Explain why isotopes having different number of neutrons are still considered to be the same element on the periodic table.

Isotopes of any given factor all incorporate the equal variety of protons, so they have the identical atomic wide variety (for example, the atomic wide variety of helium is usually 2). Isotopes of a given factor include exceptional numbers of neutrons, therefore, special isotopes have special mass numbers.

atoms of the same element with different mass are called isotopes. Atoms of the same element with same number of proton but different number of neutrons.

indium, and thallium have three electrons i think