(i) Change in colour: Reaction between lead nitrate solution and potassium iodide solution.
Pb(NO₃)₂(aq) + 2KI \(\longrightarrow \) PbI₂(s) + 2KNO₃(aq)
In this reaction, colour changes from colourless to yellow.
(ii) Change in temperature: Action of dilute sulphuric acid on zinc.
Zn(s) + H₂SO₄(aq) \(\longrightarrow \) ZnSO₄(aq) + H₂
In this reaction, heat is evolved
(iii) Formation of precipitate : Action of barium chloride on sodium sulphate.
BaCl₂(aq)+ Na₂SO₄(aq) \(\longrightarrow \) BaSO₄(s) + 2NaCl(aq)

Cold drinks contain carbon dioxide dissolved in them under pressure. Some amount of the gas escapes when a bottle of cold drink is opened while a portion of it remains dissolved. Carbon dioxide dissolved in water forms a weak acid, carbonic acid. Consumption of excess of cold drink causes accumulation of carbonic acid in the stomach which is responsible for the development of acidity.

Reaction in which a single reactant breaks down to give simpler products.
Thermal decomposition-
\(CaCO_{ 2 }\overset { \triangle }{ \longrightarrow } CaO+C{ O }_{ 2 }\)
(Or any other)
Electrolytic decomposition-
2H₂O\(\overset { Electric\quad current }{ \rightarrow } \) 2H₂+O₂
(or)
In a decomposition reaction, a single reactant breaks down into two or more simpler products.
When a decomposition reaction is carried out by heating, it is called thermal decomposition reaction.
\(\underset { (Calucium\quad carbonate) }{ CaCO_{ 3 }(s) } \overset { Heat }{ \rightarrow } \underset { Calcium\quad oxide) }{ CaO(s) } +\underset { (Carbon\quad dioxide) }{ { CO }_{ 2 }(g) } \)
When a decomposition reaction is carried out with the help of electric current, the process is called electrolysis.
\(\underset { Water }{ 2{ H }_{ 2 }O(I) } \overset { Electric\quad current }{ \longrightarrow } \underset { (Hydrogen\quad gas) }{ 2{ H }_{ 2 }(g) } +\underset { (Oxygen\quad gas) }{ { O }_{ 2 }(g) } \)

(i) Mg + 2HCl\(\rightarrow\)MgCl₂+H₂
Hydrogen gas is produced
(ii) HCl + NaOH\(\rightarrow\) NaCl+H₂O
Neutralisation reaction
(iii) 2HCI(aq)+ CaCO₃(aq)\(\rightarrow\)CaCl₂(aq)+H₂O+CO₂
Calcium chloride is formed.

Different metals react with oxygen at different rates. e.g., Sodium (Na) and potassium (K) catch fire, if left in open. Hence, these are the most reactive metals. To prevent accidental fires, these metals are kept immersed in kerosene oil. Magnesium burns in air only by heating. So, it is less reactive than sodium and potassium. Copper (Cu) does not burn on heating but blister copper burns. Hence the order of reactivity of these metals with oxygen is :
Na >Mg> Cu.
Metals react with water to produce a metal oxide and hydrogen gas. Sodium (Na) and potassium (K) react violently with cold water. So the reaction is violent and exothermic. Magnesium (Mg) does not react with cold water. It reacts with hot water. Metals like lead, copper, silver do not react with water at all. The reactivity series of metals towards water is:
Na > Mg > Cu.

(i) Bleaching powder - CaOCI₂
(ii) C(OH)₂ + Cl₂➝ CaOCI₂ + H₂O
(iii) Two uses other than disinfection are:
(a) Paper industries (b) Chemical Industries

Three properties of sodium are:
(i) Sodium is so soft that it can be cut with a knife.
(ii) It has low density.
(iii) It has low melting point.

The major differences between an electric motor and generator are stated below:
Electric Motor:
1. It converts electrical energy into mechanical energy.
2. It needs electrical energy for its works.
3. They are used as water pumps, marble grinders etc.
Generator:
1. It converts mechanical energy into electrical energy
2. It needs mechanical energy for its working.
3. They are used as water pumps, marble grinders etc.
4. diesel generator, hydro-electric generator are the examples of it.

Haematite (Fe₂O₃) is an important ore of iron.
In the upper part of the blast furnace, carbon monoxide reduces iron (III) oxide to iron metal.
\(\underset { Iron(III)oxide }{ { Fe }_{ 2 }{ O }_{ 3 } } +\underset { Carbonmonoxide }{ 3CO(g) } \rightarrow \underset { Ironmetal }{ 2Fe(I) } +\underset { Carbondioxide }{ { 3CO }_{ 2 }(g) } \)
Following reactions are involved in the blast furnace:
(i) Formation of carbon monoxide
\(\underset { Carbon }{ C(s) } +\underset { Oxygen }{ { O }_{ 2 }(g) } \rightarrow \underset { Carbondioxide }{ { CO }_{ 2 }(g) } +Heat\\ \underset { Carbondioxide }{ { CO }_{ 2 }(g) } +\underset { Coke }{ C(s) } \rightarrow \underset { Carbonmonoxide }{ 2CO(g) } \)
(ii) Reduction of iron (III) oxide or haematite to iron
\(\underset { Iron(III)oxide }{ { Fe }_{ 2 }{ O }_{ 3 } } +\underset { Carbonmonoxide }{ 3CO(g) } \rightarrow \underset { Ironmetal }{ 2Fe(I) } +\underset { Carbondioxide }{ { 3CO }_{ 2 }(g) } \)

(a) The solar cells are costly and hence the energy available from them expensive.
(b) 15 km/h is the minimum wind velocity required to obtain useful energy with a windmill.
(c) Nuclear fission is the process in which a radioactive atom splits up into smaller nuclei when struck with low energy neutrons.

Information passes through neuron in the form of electro-chemical signals. These signals are called impulse.
When an impulse reaches the end of the axon it sets off the release of some chemicals. These chemicals cross the gap or the synapse and start a similar electrical impulse in a dendrite of the next neuron. A similar synapse allows the delivery of impulses from the neurons to other cells, like muscle cells or glands.

It is given that: Voltage (V) = 2.50 V
Current (I) = 750 mA = 0.75 A
The bulb is lighted for 4 hours.
Thus,
(i) Power generated (P) = VI = 2.50\(\times\) 0.75 = 1.87 W
(ii) Resistance (R) = \(\frac { V }{ I } =\frac { 2.5 }{ 0.75 } =3.33\Omega \)
(iii) Energy consumed in 4 hours = Power\(\times\)Time = P\(\times\)t =1.87\(\times\)4 = 7.48  Wh