(i) \(\begin{bmatrix} 2H_{ 2 }O_{ 2 }\rightarrow & 2H\_ 2O+O_{ 2 } \\ 2(2+32) & 22400ml \\ =68g & (at\quad NTP) \end{bmatrix}\)
22400 ml of oxygen is obtained at NTP from = 68g of H₂0₂
10 ml of oxygen is obtained at NTP from = \(68\over22400\)x 10 .
= 0.03035 g of H₂O₂
1 ml of H₂O₂ contains = 0.03035g H₂O₂
100 ml of H₂O₂ contains = 0.03035 x 100
= 3.035g of H₂O₂
or the solution is 3.035%
or concentration of 'lO vol' solution = 3.035 x 10
= 30.35g / litre.
(ii) Normality (N) = \(Concentration \ in \ g/L \over Equivalent \ mass\)
Equivalent mass of H₂O₂ = \({Molecular \ Mass\over2}={34\over12}=17\)
\(\begin{bmatrix} 2H_{ 2 }O_{ 2 }\rightarrow & 2H\_ 2O+O_{ 2 } \\ 68g & 32 \\ ? &8g \end{bmatrix}\)
 Normality (N) = \({30.35\over17}\) = 1.785
Normality of 10 volume solution = 1.785N
[Relationship between volume strength and normality]
Let volume strength of H₂O₂ solution be 'V'.
i.e., 'V' litre of 02 is given by 1L of H₂O₂ at NTP.
g/L of H₂O₂ =\({68\over22.4}\times V\)
\(N={strength\over Equivalent \ mass }={68\over22.4}\times V \times {1\over17}\)
'V' = 5.6 x Normality
Similarly 'V' = 11.2 x molarity

Heavy water is chemically similar to ordinary water (H₂0). However D₂0 reacts more slowly than H₂0 in chemical reactions.
(i) When compounds containing hydrogen are treated with D₂0, hydrogen undergoes an exchange for deuterium
2NaOH + D₂0 \(\rightarrow\) 2NaOD + HOD
HCI + D₂0\(\rightarrow\) DCI + HOD
NH₄CI + 4D₂0 \(\rightarrow\) ND₄CI + 4HOD .
These exchange reactions are useful in determining the number of ionic hydrogens present in a given compound.
For example, when D₂0 is treated with of hypo-phosphorus acid only one hydrogen atom is exchanged with deuterium. It indicates that, it is a monobasic acid.
H₃P0₂ + D₂0 \(\rightarrow\) H₂DP0₂ + HDO
(ii) It is also used to prepare some deuterium compounds:
Al₄C₃ + 12D₂0 \(\rightarrow\) 4AI(OD)₃ + 3CD₄
CaC₂ + 2 D₂0\(\rightarrow\) Ca(OD)₂ + C2D2
Mg₃N₂ + 6D₂0 \(\rightarrow\) 3Mg(OD)₂ + 2 ND₃
Ca₃P 2+ 6D₂0\(\rightarrow\) 3Ca(OD)₂ +2PD₃

Water reacts with metals, non-metals and other compounds differently. The most reactive metals are the alkali metals. They decompose water even in cold with the evolution of hydrogen leaving an alkali solution.
2Na + 2 H₂O \(\rightarrow\) 2 NaOH + H₂
The group 2 metals (except beryllium) react in a similar way but less violently. The hydroxides are less soluble than those of Group 1.
 Ba + 2H₂O \(\rightarrow\) Ba(OH)₂ + H₂
Some transition metals react with hot water or steam to form the corresponding oxides.
For example, steam passed over red hot iron results in the formation of iron oxide with the release of hydrogen.
3Fe + 4H₂O\(\rightarrow\) Fe₃O₄ + H₂
Lead and copper decompose water only at a white heat. Silver, gold, mercury and platinum do not have any effect on water. In the elemental form, the non-metals such as carbon, sulphur and phosphorus normally do not react with water. However, carbon will react with steam when it is red (or white) hot to give water gas.

(i) Hard water is harmful for boilers, because of deposition of salts in the form of scale. This reduces the efficiency of the boilers.
(ii) Hard water forms scum/precipitate with soap. Soap containing sodium stearate
(C₁₇ H₃₅ COONa) reacts with hard water to precipitate out Ca/Mg stearate.
2C₁₇H₃₅COONa_(aq) + M²⁺_(aq)➝ (C₁₇H₃₅COO)2M↓2Na⁺_(aq); M is Ca/Mg
It is, therefore, unsuitable for laundry.

Hydrogen is conveniently prepared in laboratory by the reaction of metals, such as zinc, iron, tin with dilute acid.
\(\mathrm{Zn}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2} \uparrow\)