EVERYDAY SCIENCE

Detailed explanation-1: -An element is a pure substance and is made of only one type of atom; it cannot be broken down into a simpler substance.

Detailed explanation-2: -Atoms of the same chemical element do not always have the same mass because, although the number of protons in the nucleus is the same for all atoms of the same element, the number of neutrons is not. Most elements as they occur naturally on earth are mixtures of several isotopes.

Detailed explanation-3: -Atoms of the same element have the same atomic number so the number of protons (and electrons) are same. But they have same or different mass numbers (like that for isotopes). Different mass number will have different number of neutrons.