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

(a) 24 g of Mg = 6.022 x 10²³ particles
48 g of Mg =  12.044 x 10²³ particles
(b) 32 g of O₂ = 6.022 x 10²³ particles
8 g of O = 1.50 x 10²³ particles
(c) 1 mole of carbon = 6.022 x 10²³ particles
0.1 mole of carbon = 6.022 x 10²³ particles

(i) Al₂(SO₄)₃ - Aluminium sulphate
(ii) CaCl₂ - Calcium chloride
(iii) K₂SO₄ - Potassium sulphate
(vi) KNO₃ - Potassium nitrate
(v) CaCO₃ - Calcium carbonate

An atom is the smallest particle of an element which may or may not have independent existence.On the other hand,'molecule' is the smallest particle of the element or compound which is capable of independent existence.For example helium (He) is an atom and can exist as such, whereas hydrogen atom cannot exist as such but exists as a molecule, i.e H₂ .A molecule may be made up of similar atoms or dissimilar atoms.

The above experiment illustrates law of multiple proportions 16 g and 32 g of oxygen respectively are required to combine with a fixed weight, i.e 12 g of carbon to form carbon monoxide and carbon monoxide and carbon dioxide.The ratio of oxygen which combines with a fixed weight of carbon 16 : 32 or 1 : 2 a simple whole number.This is law of multiple proportions.

1 mole of aluminium oxide, Al₂O₃ = 2  x 27 + 3 x 16 = 102 u = 102 g
102 g Al₂O₃ has = 6.023 x 10²³ Al₂O₃ molecules
0.051  g Al₂O₃ has = \(\frac { 6.023\times { 10 }^{ 23 } }{ 102 } \)
= 3.01 x 10²⁰ Al₂O₃ molecuels
1 molecule of Al₂O₃ gives = 2Al⁺⁺⁺ ions
Hence 0.051 g Al₂O₃ gives = 2 x 3.01 x 10²⁰ Al⁺⁺⁺ ions
=6.023 x 10²³ aluminium ions.

Number of atoms in 23 g of sodium =6.022 x 10²³
Number of atoms in 11.5 g of sodium = \(\frac { 11.5 }{ 23 } \times 6.022\times { 10 }^{ 23 }\)
=3.011 x 10²³ atoms
Number of atoms in 40 g of calcium = 6.022 x 10²³
Number of atoms in 15 g of calcium = \(\frac { 6.022\times { 10 }^{ 23 }\times 15 }{ 40 } \)
=2.25 x 10²³ atoms.
Therefore, 11.5g of sodium has more number of atoms than in 15g of calcium

1 mole = atomic mass = 6.022 x 10²³ atoms
Now mass of one atom of M = 3.05 x 10^-22
Now mass of 6.022 x 10²³ atoms of M =  3.05 x 10^-22 x  6.022 x 10²³ g = 183.7 g
Mass of 1 mole or atomic mass of M = 183.7 g
This could be tungeten (W)

(i) 1 Mole of Carbon atom = 6.022 x 10²³ atoms
6.022 x 10²³ atoms of carbon weigh = 12 g
1 atom of carbon weighs = \(\frac { 12 }{ 6.022\times { 10 }^{ 23 } } \\ \)  
= 1.99 x 10^-23
(ii) (a) n = 0.5 mol; M = 14 x 2 = 28 g; m = ?
m = n x M = 0.5 x 28 = 14.0 g
(b) n = 0.2 mol; M = 16 g; m = ?
m = n x M = 0.2 x 16 = 3.2 g
(c) n = 4 mol; M = 27 g; m = ?
m = n x M = 4 x 27 = 108 g

(i) Mass of 1 mole CO₂ = 12 + 32 = 44 u
Mass of 5 moles CO₂ = 44 x 5 = 220 u
Mass of 1 mole of H₂O = 2 + 16 = 18 u
Mass of 5 moles of H₂O = 5 x 18 = 90 u
(ii) 40 g calcium make = 1 mole
240 g calcium make = \(\frac { 240 }{ 40 } \) = 6 moles
24 g magnesium make = 1 mole
240 g magnesium make = \(\frac { 240 }{ 24 } \) = 10 moles
Ratio of 240 g calcium and 240 g magnesium in moles = \(\frac { 6 }{ 10 } \) or 3 : 5

The mass of 1 mole of nitrogen atoms is 14 g.