The correct option is (c).
Explanation
The fundamental properties of an atom are determined by the composition of its nucleus, specifically the number of protons and neutrons. These subatomic particles define the atomic number and mass number, which are crucial for identifying elements and their isotopes.
Statement-wise Analysis:
- Statement 1 is Incorrect: The Atomic Number (denoted by 'Z') is defined as the total number of protons present in the nucleus of an atom. It is not determined by the number of neutrons. For a neutral atom, the number of protons is equal to the number of electrons.
- Statement 2 is Correct: The Mass Number (denoted by 'A') is the sum of the total number of protons and neutrons present in the nucleus of an atom. Protons and neutrons are collectively referred to as nucleons. Therefore, Mass Number (A) = Number of Protons (Z) + Number of Neutrons (n).
- Statement 3 is Correct: Elements are defined strictly by the number of protons they possess (Atomic Number). While the number of neutrons can vary within the same element (creating isotopes) and the number of electrons can change (creating ions), the number of protons remains constant for a specific element.
Key Takeaway:
The identity of an element is determined by its Atomic Number (Z), which equals the number of protons. The Mass Number (A) represents the total mass of the nucleus, calculated as the sum of protons and neutrons.