Question

With the help of given Table, find out the mass number of oxygen.

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				Valency
						K	L	M	N
Hydrogen	H	1	1	-	1	1	-	-	-	1
Helium	He	2	2	2	2	2	-	-	-	0
Lithium	Li	3	3	4	3	2	1	-	-	1
Beryllium	Be	4	4	5	4	2	2	-	-	2
Boron	B	5	5	6	5	2	3	-	-	3
Carbon	C	6	6	6	6	2	4	-	-	4
Nitrogen	N	7	7	7	7	2	5	-	-	3
Oxygen	O	8	8	8	8	2	6	-	-	2
Fluorine	F	9	9	10	9	2	7	-	-	1
Neon	Ne	10	10	10	10	2	8	-	-	0
Sodium	Na	11	11	12	11	2	8	1	-	1
Magnesium	Mg	12	12	12	12	2	8	2	-	2
Aluminium	Al	13	13	14	13	2	8	3	-	3
Silicon	Si	14	14	14	14	2	8	4	-	4
Phosphorus	P	15	15	16	15	2	8	5	-	3.5
Sulphur	S	16	16	16	16	2	8	6	-	2
Chlorine	Cl	17	17	18	17	2	8	7	-	1
Argon	Ar	18	18	22	18	2	8	8		0

Answer 1

The number of protons and neutrons present in the nucleus of an atom is called mass number.

That is, mass number = number of protons + number of neutrons

Mass number = 8 + 8

= 16

Sulfur protons = 16, neutrons = 16

Mass number = 16 + 16

= 32