Question

what are isotopes?
isotopes are different phases of built from the equivalent atoms of the same element.
isotopes are the chemical elements which are in the same group in the periodic table.
isotopes are atoms of the same element that have different masses because they contain a different number of neutrons.
isotopes are atoms of different elements that have equal masses because they contain a different number of neutrons.

Explanation:

Isotopes are defined as atoms of the same element. They share the same number of protons (which defines the element) but have different numbers of neutrons. This difference in neutron count leads to different atomic masses. Let's analyze each option:

• Option 1: Isotopes are not about phases. Phases (like solid, liquid, gas) are physical states, not related to isotopic definition.
• Option 2: Isotopes are not different elements. Elements in the same group have similar chemical properties due to valence - electron configuration, but isotopes are within one element.
• Option 3: This matches the definition. Same element (same proton number), different neutrons (so different mass).
• Option 4: Isotopes are of the same element, not different elements.

Answer:

Isotopes are atoms of the same element that have different masses because they contain a different number of neutrons.