Required Answers:-

1. Rusting is the process in which a brown layer gets deposited on the surface of the iron due to the reaction of oxygen and moisture from air.

The two essential conditions for rusting are as follows:-

• Presence of oxygen in air
• Presence of moisture in air.

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2. Symbol of the given elements are as follows:-

• Bromine - Br
• Helium - He
• Potassium - K
• Sodium - Na
• Mercury - Hg

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3. Compounds:-

• Water
• Carbon-dioxide
• Sodium Chloride.

Elements:-

• Nitrogen
• Zinc
• Aluminium

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4. Crystallization: The process by which a substance in liquid state is converted into it's solid form.

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5. Chemical formula of the following compounds are as follows:-

• Sulphuric Acid - H₂SO₄
• Zinc Sulphate - ZnSO₄
• Silver Nitrate - AgNO₃
• Calcium Carbonate - Ca(CO)₃

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6. (a) S + O₂ → SO₂

⇒ This reaction is a type of combination reaction as well as oxidation reaction.

• Combination reaction because two substances are combining to form a single substance.
• Oxidation reaction because Sulphur is gaining oxygen.

(b) CaCO₃ → CaO + CO₂

⇒ This reaction is a type of decomposition reaction.

• Decomposition reaction because one single substance is decomposing to form two new substances.

(c) HCl + NaOH → NaCl + H₂O

⇒ This reaction is a type of neutralization reaction.

• Neutralization reaction because HCl is an acid and NaOH is a base. When an acid reacts with base a salt is formed.

(d) NH₄NO₃ + NaCl → NaNO₃ + NH₄Cl

⇒ This is a type of double - displacement reaction.

• Double - displacement reaction because exchange of ions between Sodium and Ammonia has taken place.

(e) Zn + FeSO₄ → ZnSO₄ + Fe

⇒ This is a type of displacement reaction.

• Displacement reaction because here zinc displace iron in a solution.

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7. (a) CaO + H₂O → Ca(OH)₂

→ The equation is already balanced. The number of atoms of each element on both product and reactant sides are equal.

(b) H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

→ The equation is already balanced. The number of atoms of each element on both product and reactant sides are equal.

(c) H₂ + Cl₂ → 2HCl

→ The equation is already balanced. The number of atoms of each element on both product and reactant sides are equal.

(d) H₂ + O₂ → 2H₂O

→ Here we can see that number of hydrogen atom on LHS is 2 and the number of atoms of hydrogen on RHS is 4. So let us add 2 infront of hydrogen on LHS.

Balanced equation:-

⇒ 2H₂ + O₂ → 2H₂O

(e) Mg + O₂ → MgO

→ Here we can see that number of atoms in oxygen on LHS is 2 while on RHS is 1. So let us put 2 infront of MgO

New equation:-

⇒ Mg + O₂ → 2MgO

Still the equation is not balanced as number of atoms in magnesium on LHS is 1 while on RHS is 2. So let us put 2 infront of Mg on LHS.

Balanced equation:-

⇒ 2Mg + O₂ → 2MgO

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Verified answer

1. What is rusting of iron ? What are the two essential conditions for rusting ?

Ans - Rusting of iron refers to the formation of rust, a mixture of iron oxides, on the surface of ironobjects or structures. This rust is formed from a redox reaction between oxygen and iron in an environment containing water (such as air containing high levels of moisture).

Rusting of iron takes place in the presence of moisture and air. So the presence of air and water vapour in air are two necessary conditions for rusting of iron.

2. Give the symbols of following elements:

(a) Bromine :- Br

(b) Helium :- He

(c) Potassium :- K

(d) Sodium :- Na

(e) Mercury :- Hg

3. Classify the following as elements or compounds: water, nitrogen, zinc, carbon dioxide, sodium chloride, aluminium.

Ans - Elements → 

 → The elements are regarded as the building blocks of the universe.

Nitrogen, Zinc and Aluminium are elements.

Compounds → 

→ It is a pure substance made up of two or more elements chemically combined in a fixed proportion by mass.

Water, Carbon dioxide and Sodium Chloride are compounds.

4. What do you understand by crystallization ?

Ans - Crystallization or crystallisation is the process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some of the ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a gas.

5. Write the chemical formula of following compounds:

(a) Sulphuric acid :- H₂SO₄

(b) Zinc sulphate :- ZnSO₄

(c) Silver nitrate :- AgNO3

(d) Calcium carbonate :- CaCO3

6. Identify the type of reaction

(a) S + 0₂ → SO₂ - Combination Reaction

(b) CaCO₃ → CaO + CO₂ - Decomposition Reaction

(c) HCl + NaOH → NaCI + H₂O - Neutralization Reaction

(d) NH₄NO₃ + NaCl → NaNO₃ + NH₄CI - Chemical Reaction

(e) Zn + FeSO₄ → ZnSO₄ + Fe - Zn is a reducing agent, FeSO4is an oxidizing agent.