(a) CCarbon combines with 4/3 times it mass of oxygen, so atomic mass of oxygen atom is \({4\over3}\times{12\over1}=16u\) Now since equal masses of sulphur and oxygen molecule combine to form SO₂, atomic mass of sulphur is 16 x 2 = 32u.
(b) In earlier times, in the absence of weights, things were sold with reference to some other small substance.It was not successful because different people used different substance as reference material.

To react with 14 g nitrogen, mass of hydrogen required = 3 g
Tor react with 42 g nitrogen, mass of hydrogen required = \(\frac { 3 }{ 14 } \times 42\) = 9g

1 mole of S₈ = 32 x 8 = 256 g
1 mole of S₈ = 6.023 x 10²³ molecules
256 g S₈ has =  6.023 x 10²³ S₈ molecules
16 g S has = \(\frac { 6.023\times { 10 }^{ 23 } }{ 256 } \times 16=3.76\times { 10 }^{ 22 }\)molecules

% of boron in the sample = \(\frac { 0.096 }{ 0.24 } \times 100\) = 40%
and % of oxygen in the sample = \(\frac { 0.144 }{ 0.24 } \times 100\)= 60 %
The sample of compound containes 40% boron and 60% oxygen by weight

1 mole of an element 'X' contains 6.022 x 10²³ atoms
Now weight of 1.66 x 10²⁰ atoms = 16.26 x 10^-3 g
Mass of  6.022 x 10²³ atoms = \(\frac { 16.26\times { 10 }^{ -3 } }{ 1.66\times { 10 }^{ 20 } } \) x 6.02 x 10²³ = 59 g
The atomic mass of element 'X' is 59 u

Atomic mass of zinc = 65.37 g
65.37 g of zinc contains = 1 mole of zinc = 6.023 x 10²³ atoms of Zn
1 g of zinc will contain = \(\frac { 6.023\times { 10 }^{ 23 } }{ 65.37 } \)= 9.21 x 10²¹ atoms.
1 atom of zinc = \(\frac { 1 }{ 9.21\times { 10 }^{ 21 } } \)= 1.08 x 10^-22 g.

(i) Molecular mass of HNO₃ = 1 x 40 + 1 x 12 + 3 x 16 = 100u
(ii) Molecular mass of = 1 x 12 + 3 x 1 + x 12 + 1 x 16 + 1 x 16 + 1 x 1 = 60g

When hydrogen is 1 g, amount of oxygen in water = 8g
Number of atoms of hydrogen in 1 g = 6.022 x 10²³
Number of atoms of oxygen in 8 g = \(\frac { { 6.022\times 10 }^{ 23 } }{ 16 } \times 8\)
= 3.022 x 10²³
Ratio of hydrogen and oxygen in water = \(\frac { { 6.022\times 10 }^{ 23 } }{ { 3.022\times 10 }^{ 23 } } \) = 2 : 1

Atomic mass of any substance indicates the times it is heavier than 1/12th of C-12 atom.Now  atomic mass of H atom is one u, it means that one C-12 atom is 12 times as heavy as one H atom or to say 1000 C-12 atoms are 12 times as heavy as 1000 h atoms or 6.022 x 10²³ C-12 atoms are 12 times as heavy  6.022 x 10²³ atoms.Since atomic mass of C-12 is 12u and that of H atoms is 1 u, it can be inferred that weight equal to atomic mass of C-12 or H-atom contains the same number of atoms.Thus, it can be shown that gram atomic mass or gram molecular mass of all substance have the same number, i,.e 6.022 x 10²³ particles.

Since M has a valancy of +1
Chemical formula of chloride of M = MCl
Chemical formula of bicarbonate of M = MHCO₃
Chemical formula of sulphide of M = M₂S

Compounds containing charged species are known as ionic compounds.Such compounds are formed from combination of metals with non-meatls.For example, sodium chloride is an ionic compound.Its constituent particles charged sodium ions and negatively charged chloride ions.

An atom is a building block of an element.It is very very small, so small that millions of atoms when stacked would hardly make a layer as thick as thin sheet of paper.The radius of an atom of hydrogen is 10^-10 m or 10^-1 nm, one molecule of water is 1 nm.Compared to it grain of sand is 10^-4 m.