Define (i) atomic number (ii) mass number. Give their symbols.

1.	Define (i) atomic number (ii) mass number. Give their symbols.
Answer» 1. The number of protons in the nucleus of an atom of an element is called the atomic number of the element. It is also known as the proton number. It is denoted by Z. 2. The number of nucleons (protons and neutrons) in the nucleus of an atom is called the mass number or the atomic mass number. It is denoted by A. [Notes : (i) The number of neutrons in the nucleus of an atom is known as the neutron number, denoted by N. It is usually greater than Z, with the exceptions of helium (2 protons, 2 neutrons) and hydrogen (1 proton, no neutron) (ii) A = Z + N.]

Answer»

1. The number of protons in the nucleus of an atom of an element is called the atomic number of the element. It is also known as the proton number. It is denoted by Z.

2. The number of nucleons (protons and neutrons) in the nucleus of an atom is called the mass number or the atomic mass number. It is denoted by A.

[Notes : (i) The number of neutrons in the nucleus of an atom is known as the neutron number, denoted by N. It is usually greater than Z, with the exceptions of helium (2 protons, 2 neutrons) and hydrogen (1 proton, no neutron) (ii) A = Z + N.]

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