\(Equivalent \ mass ={sum \ of \ the \ atomic \ masses \ of \ atoms \ present \ in \ the \ ion \over charge \ on \ the \ ion}\)
For CO₃ ^-2 ion
\(Equivalent \ mass ={1 x atomic \ mass \ of C + 3 x atomic \ mass \ of 'O'\over 2}\)
\(={12+3\times 16\over 2}={60\over2}=30\ g\ eq^{-1}\)

Stoichiometry gives the numerical relationship between chemical quantities in a balanced chemical equation.

2 mole of H₂ react with 1mole of O₂.
1.5 mole of H react with 0.75 mole of O₂.
Excess O₂ = 0.9062 - 0.75 = 0.1562 mol.

S₂O₃^-2 (S in S₂O₃^-2)
Oxidation number of sulphur = x
Oxidation number of oxygen = - 2
2x + 3 (- 2)  \(\Rightarrow\) 2x - 6 = - 2 (or) 2x ~ 4 or x = +2
Hence, the oxidation number of sulphur is S₂O₃^-2 is + 2.

Molar Mass of ferrous Sulphate = \(\begin{cases} atomic\ \ mass\ of\ Fe+atomic\ mass\ of\ s' \\ +4x\ atomic\ mass\ of\ O\ \end{cases}\)
= 56 + 32 + 4 x 16 = 152
In reactions, Fe⁺² ion is oxidised to Fe⁺³ ion Fe⁺² \(\rightarrow\) Fe⁺³ + e
equivalent mass = \(\frac { Molar\quad mass }{ no\quad of\quad involved } =\frac { 152 }{ 1 } =152g{ eq }^{ -1 }\)

molar mass of crystalline oxalic acid (H₂C₂O₄.2H₂o) = Molar Mass of ocalic acid + 2 x Molar mass of H₂o
= 90 + 2 x 18 = 126
Bascity = 2
\(\therefore\) \(\begin{matrix} W\ equivalent\ \ mass\ of \\ crystalline\ \ oxalic\ \ acid \end{matrix}\} =\frac { 126 }{ 2 } =63g\) eq^-1

The mass of an atom (10^-27 kg) is too small to be measured directly. They are measured with reference to a standard atom, Hence they are called as relative atomic masses.

(iii) \(\overset { 0 }{ \underset { \underset { 2e^{ - } }{ \downarrow } }{ Cu } } { O }_{ 7 }+H\overset { +5 }{ \underset { { 1e }^{ - } }{ \underset { \uparrow }{ N } } } { O }_{ 3 }\longrightarrow \overset { +2 }{ Cu } \left( { No }_{ 3 } \right) _{ 2 }+\overset { +4 }{ N } { O }_{ 2 }+{ H }_{ 2 }O\)
Cu +2HNO₃ \(\longrightarrow \)  Cu(NO₃)₂ + NO₂ + H₂O
Cu + 2HNO₃ + 2HNO₃ \(\longrightarrow \) Cu(NO₃)₂ + 2NO₂ + 2H₂O
Cu + 4HNO₃ \(\longrightarrow \) Cu (NO₃)₂ + 2No₂ + 2H₂O

 (ii) \({ K }\overset { +7 }{ \underset { \underset { 3e^{ - } }{ \uparrow } }{ M } } n{ O }_{ 4 }+{ Na }_{ 2 }\overset { +4 }{ \underset { { 2e }^{ - } }{ \underset { \downarrow }{ S } } } { O }_{ 3 }\longrightarrow \overset { +4 }{ M } { nO }_{ 2 }+{ Na }_{ 2 }\overset { +6 }{ s } { O }_{ 4 }+KOH\)
\(\Rightarrow\) 2KMnO₄ + 3Na₂SO₃ \(\longrightarrow \)   MnO₂ + Na₂SO₄ + KOH
\(\Rightarrow\) 2KMnO₄ + 3Na₂SO₃ \(\longrightarrow \)  2MnO₂ + 3Na₂SO₄ + KOH
\(\Rightarrow\) 2KMNO₄ + 3NaSO₃ + H₂O \(\longrightarrow \) 2MnO₂ + ₃Na₂SO₄ +2KOH

It is defined as the imaginary charge left on the atom when all other atoms of the compound have been removed in their usual oxidation states that are assigned according to set of rules.

Gram equivalent mass of an element, compound or ion is the mass that combines or displaces 1.008 g hydrogen or 8 g oxygen or 35.5 g chlorine.

One mole is the amount of substance of a system, which contains as many elementary particles as there are atoms in 12 g of carbon -12 isotope.

\(\overset { o }{ Z } n\longrightarrow { Z }n^{ 2+ }\)
\(\overset { +5 }{ N } { O }_{ 3 }^{ - }\longrightarrow \overset { 2+ }{ NO } \)
(1) \(\Rightarrow \) Zn \(\rightarrow\) Zn²⁺ +2e^-                                  .....(3)
(2) \(\Rightarrow \) \({ NO }_{ 3 }^{ - }+{ 3e }^{ - }+{ 4H }^{ + }\longrightarrow NO+{ 2H }_{ 2 }O\)......(4)