HomeQ&AWith the help of the given table, find out the mass number of oxygen and sulphur atom. Table: Composition of Atoms of the First Eighteen Elements with Electron Distribution in Various Shells. Name of Element Symbol Atomic number Number of Protons Number of Neutrons Number of electrons Distribution of electrons K L M N Valency Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium H He Li Be B C N O F Ne Na Mg 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 – 2 4 5 6 6 7 8 10 10 12 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 2 2 2 2 2 2 2 2 2 2 – – 1 2 3 4 5 6 7 8 8 8 – – – – – – – – – – 1 2 – – – – – – – – – — – – 1 0 1 2 3 4 3 2 1 0 1 2 Aluminium Silicon Phosphorus Sulphur Chlorine Argon Al Si P S Cl Ar 13 14 15 16 17 18 13 14 15 16 17 18 14 14 16 16 18 22 13 14 15 16 17 18 2 2 2 2 2 2 8 8 8 8 8 8 3 4 5 6 7 8 – – – – – 3 4 3,5 2 1 0

With the help of the given table, find out the mass number of oxygen and sulphur atom. Table: Composition of Atoms of the First Eighteen Elements with Electron Distribution in Various Shells. Name of Element Symbol Atomic number Number of Protons Number of Neutrons Number of electrons Distribution of electrons K L M N Valency Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium H He Li Be B C N O F Ne Na Mg 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 – 2 4 5 6 6 7 8 10 10 12 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 2 2 2 2 2 2 2 2 2 2 – – 1 2 3 4 5 6 7 8 8 8 – – – – – – – – – – 1 2 – – – – – – – – – — – – 1 0 1 2 3 4 3 2 1 0 1 2 Aluminium Silicon Phosphorus Sulphur Chlorine Argon Al Si P S Cl Ar 13 14 15 16 17 18 13 14 15 16 17 18 14 14 16 16 18 22 13 14 15 16 17 18 2 2 2 2 2 2 8 8 8 8 8 8 3 4 5 6 7 8 – – – – – 3 4 3,5 2 1 0

ScienceClass 9CBSEAnswered 27 Mar 2026

Answer

Solution:

(a) To find the mass number of Oxygen,

Number of protons = 8

Number of neutrons = 8

Atomic number = 8

Atomic mass number = Number of protons + number of neutrons = 8 + 8 = 16

Therefore, the mass number of oxygen = 16

(b) To find the mass number of Sulphur,

Number of protons = 16

Number of neutrons = 16

Atomic number = 16

Atomic mass number = Number of protons + number of neutrons = 16 + 16 = 32

Science · Class 9

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