Hydrogen gas and zinc sulphate are formed when zinc granules are treated with sulphuric acid
\(\underset{Zinc }{Zn(s)}+\underset{Sulphuric\ acid}{H2SO4(l)} \rightarrow\underset{Zinc\ sulphate}{ZnSO_4(aq)}+\underset{Hydrogen}{H_2(g)}\)
Zinc chloride and hydrogen gas are formed, when zinc granules are treated with hydrochloric acid.
\(\underset{Zinc}{Zn(s)} + \underset{Hydrochloric\ acid}{2HCI(l)}\rightarrow \underset{Zinc}{ZnCI2(s)} +\underset{Water}{ H_2(g)}\)
Similarly, hydrogen gas and zinc nitrate are formed when zinc granules are treated with nitric acid.
\(\underset{Zinc}{Zn(s)} + \underset{Nitricic\ acid}{2HNO_3(l)}\rightarrow \underset{Zinc\ nitrate}{Zn(NO_3)_2(s)} +\underset{Hydrogen}{ H_2}\)
Since, zinc is less reactive than sodium, thus no reaction takes place when zinc granules are treated with sodium chloride.
Sodium zinc ate and hydrogen gas are formed when zinc granules are treated with sodium hydroxide and water.
\(Zn + 2H_2O + 2NaOH\rightarrow Na_2Zn(OH) _4 + H_2\)

(a) Carbon dioxide turns lime water milky as it forms calcium carbonate with lime water. This is the characteristics test for carbon dioxide.
Ca(OH)₂ + CO₂ --> CaCO₃ + H₂O
(b) The smell of sulphur dioxide gas is like burning of sulphur, which is the characteristics test for sulphur dioxide. Sulphur dioxide turns moist litmus paper from blue to red.
(c) When a burnt candle or match stick is brought near the oxygen gas, it starts burning brightly. This is the characteristic test for oxygen gas.
(d) When a burnt candle or match stick is brought near the hydrogen gas, it burns with pop sound, which is the characteristic test for hydrogen gas.

MnO₂ + 4HCl \(\rightarrow\) MnCl₂ + Cl₂ + 2H₂O

Aluminium powder is the reducing agent that may be used to obtain manganese from manganese dioxide.

(i) CaCO₃(s) + 2HCl(aq) \(\longrightarrow \) CaCl₂(s)+ H₂O(I) + CO₂(g)
(ii) 2Al(s) + 6HCl(aq)\(\longrightarrow \) 2AlCI₃(aq) + 3H₂(g)
(iii) MnO₂ + 4HCl(aq) \(\longrightarrow \) MnCl₂ + 2H₂0(I) +Cl₂(g)

(i) Substance X-Calcium Hydroxide.
Ca(OH)₂(aq) + CO₂(g)\(\longrightarrow \) CaCO₃(s) + H₂Cl
                                             (White ppt.)
(ii) Calcium hydroxide is obtained by reaction of calcium oxide and water.
CaO(s) + H₂O(l) \(\longrightarrow \)Ca(OH)₂(aq) + Heat

(i) Before heating, it is pale green.
After heating, it is brown or reddish brown.
Two observations are:
(a) Change in state and colour
(b) Evolution of gas
(ii) Decomposition reaction
2FeSO₄(s) \(\overset { Heat }{ \rightarrow } \) Fe₂O₃(s) + S0₂(g) + SO₃(g) 

N₂ + H₂ \(\rightarrow \)  NH₃ (Unbalanced equation).
(i) Examine the number of atoms of different elements present in the unbalanced equation.
(ii) In the above reaction, left hand N₂ and H₂ of both the sides are unbalanced.
(iii) To balance hydrogen, H₂ is multiplied by 3 on side. It makes 6H-atoms on the left hand side.
(iv) Now to balance hydrogen atoms on the right hand side, NH₃ should be multiplied by 2. It makes 6H-atoms on this side.
(v) Now to balance nitrogen atoms, they are counted separately for both the sides and we will find that, nitrogen atoms are 2 on both the sides.
(vi) Balanced chemical equation will be :
N₂ + H₂ \(\rightarrow \)  NH₃.