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No, the handle and bristles of a tooth brush should be made of different materials. The handle of a toothbrush should be hard and strong so, it should be made from plastic. While the bristles should be soft and flexible so, they should be made from nylon

(a) Aluminium.

(b) Oxygen.

Metal – Mercury.

Non metal – Bromine.

Metals are electropositive elements because they can form positive ions by losing electrons. Non-metals are electronegative elements because they can form negative ions by gaining electrons.

3. Heating anhydrous HF and MnO₂  

The processes of loosing water of crystallization, when the substance is exposed to air for long time to form anhydrous or monohydric substance is called as efflorescence.

Na₂CO₃ 10 H₂O, Sodium carbonate deca hydrate is one example.

Na₂CO₃ , 10 H₂O -------------->Na₂CO₃ H₂O + 9H₂O

Correct option is d) 2, 8, 1

There is no cavity inside the ball.

The main limitation of J.J. Thomson’s model of atom was that he is unable to explain, how the positively charged particles are shielded from negatively charged particles without getting neutralized.

The negative and positive charges are equal in magnitude are present in atom. So, the atom as a whole is electrically neutral as whole according to Thomson model.

In Thomson’s model the distribution of atomic mass is uniform. Dalton’s atomic theory does not say anything about atomic mass distribution.

Bohr-Bury proposed the following rules for electron distribution. 

Rule – 1 :

The maximum number of electrons that can be accommodated in each shell is given by a formula 2n2. Where n is the shell number, which takes the values 1, 2, 3,…. 

Ex : For K shell, n = 1

∴ Maximum number of electrons in K shell = 2(1)2 = 2 × 1=2 

Rule – 2 : 

Each energy level or electron shell is further divided into subshell. The maximum number of electrons that can be accommodated in each subshell is 8.

Rule – 3: 

Electron cannot be filled in a given shell unless the inner shells are completely filled.

• The revolving electron would lose energy continuously and get directed towards positively charged nucleus and eventually crash into the nucleus. 
• If this is true, the atoms would become highly unstable and the matter would not exist, but matter exists.

1. Dalton’s atomic model: 

Dalton’s atomic theory does not tell anything about the structure of the atom. There is no mention of electron in Dalton’s atomic theory

Rutherford’s atomic model: 

Rutherford’s atomic model tells about the structure of the atom, i.e. the electron revolving around the nucleus.

2. Thomson’s atomic model: 

The electrons are embedded in a gel of positive charge. Here the electrons are stationary and there is no concept of nucleus.

Rutherford’s atomic model: 

In Rutherford’s atomic model, the electrons are not stationary, they revolve around the nucleus which is positively charged.

Isotopes of the element have the same chemical properties.

Correct option is (d) protons and neutrons

In 1909, Rutherford proposed a model of atom based on the alpha particle scattering experiment. 

The main features are

1.  All the positively charged material in an atom formed a small dense centre, called the nucleus of the atom. The electrons were not a part of nucleus. 
2.  The negatively charged electrons revolve around the nucleus in well-defined orbits. 
3.  The size of the nucleus is very small as compared to the size of the atom. 

This model is known as planetary model because the electrons revolve around the nucleus as planets revolve around the sun. 

This model failed to explain the stability of atom.

Correct option is (c) electrons

Hydrogen, deuterium, tritium.

• According to Dalton, atom is indivisible. 
• But Michael Faraday’s experiments on electrolysis proved that atoms were acquiring negative charge during electrolysis. 
• This is contradiction to Dalton’s theory. 
• This lead to an idea that there must exist some tiny particles in atom which are responsible for atom to behave sometimes as charged particles. 
• As atom is considered as electrically neutral, it probably had equal number of positive and negative constituents to maintain electrical neutrality.
• This gave scope to think about sub-atomic particles.

Average atomic mass of Bromine =

 \(\frac{49.7}{100}\,\times\,79\,+\,\frac{50.3}{100}\,\times\,81 = 39.263\,+\,40.743=80.006\,g.\)

Applications of isotopes :

1.  Some isotopes are used for solving chemical and medical mysteries. 
2.  Isotopes are also commonly used in the laboratory to investigate the steps of a chemical reaction. 
3.  The isotope of uranium is used as a fuel in nuclear reactors. 
4.  The isotope of iodine is used in the treatment of goitre. 
5.  The isotope of cobalt is used in the treatment of cancer.

• In nature, most elements occur as a mixture of two or more isotopes, each isotope has a certain percentage of natural occurrence. 
• The atomic mass of an element is taken as an average mass of all the naturally occuring atoms of the sample element. Ex : Let us calculate the atomic mass of chlorine.
•  Isotope of Cl occurs in nature, in two isotopic forms, with masses 35 units and 37 units. 
• The isotope with mass 35 is present in 75% in nature. The isotope with mass 37 is present in 25% in nature. 
• The average mass of chlorine is \(=[(\,35\,\times\frac{75}{100})\,+\,(\,35\times\frac{25}{100})] =(\frac{105}{4}\,+\,\frac{37}{4}) = \frac{142}{4}=35.5\,units.\)

Correct option is (c) neutrons

Correct option is a. 153.12 g of KCIO₃

Main constituent of LPG is Butane

Density of gold coloured metal object

= \(\frac{Mass}{Volume}\)

= \(\frac{365\,g}{22.12\,cm^3}\)

= 16.50 g cm³

\(\because\) The density of pure gold is 19.32 g/cm³. So, this object is not composed of pure gold.

1. The loss of water in the form of vapour is called transpiration. 

2. Stomatal transpiration is a main type of transpiration where minute pores are concerned with it. 

3. Stomata are bounded by two guard cells which in turn are surrounded by accessory cells. 

4. Opening and closing of stomata is controlled by turgidity of guard cells. 

5. When guard cells become turgid due to endosmosis their lateral thin and elastic wall bulges or stretch out. 

6. The inner thick and inelastic wall is pulled apart, thus the stoma opens during daytime

7. At night when guard cells become flaccid due to exosmosis the wall relaxes and stoma closes. 

8. Endosmosis and exosmosis takes place due to changes in osmotic potential of guard cells.

N₂ + 3H₂ → 2NH₃

(i) 1 mole N₂ requires 3 moles of H₂

\(\because\)  28 kg N₂ require 6 kg H₂

\(\therefore\) 25 kg N₂ will require = \(\frac{6}{28}\) x 25 = 5.36 kg H₂

Hence, N₂ is the limiting reagent.

(ii) 1 N₂ produces 2 moles NH₃

\(\because\)  28 kg N₂ produce 34 moles NH₃

\(\therefore\) 25 kg N₂ will produce = \(\frac{34}{28}\) x 25

= 30.26 kg NH₃

N₂(g) + 3H₂(g) → 2NH₃(g)

\(\because\) 1 L of N₂ reacts with 3 L of H₂.

\(\therefore\) 2 L of N₂ will react with 6 L of H₂, but we have only 2 L of H₂, So, H₂ is the limiting reagent.

\(\because\) 3 L of H₂ gives 2 L of NH₃

\(\therefore\)  2 L of H₂ will give = \(\frac{2}{3}\) x 2 = \(\frac{4}{3}\) = 1.33 L of NH₃

Yes, it can be reversed by unfolding the dress.

Formation of day and night, occurrence of seasons are periodic changes.

1. If we observe that every change mentioned is the table repeats after some period of time. 

2. Such changes are known as periodic changes.

3. The events which repeat at regular intervals of time are called periodic events.

Changes which do not occur at regular intervals of time and which cannot be predicted are called non periodic changes.

The changes are repeating at regular intervals of time and which can be predicted are called periodic changes.

The reaction of iron (III) oxide (Fe₂O₃), with aluminium, is used to join railings of railway tracks or cracked machine parts. This reaction is known as the thermite reaction.

FeO₃ + 3CO → 2Fe + 3CO₂

\(\because\) Moles of CO are used to make 2 moles of Fe

\(\therefore\) 16 moles of CO will be used to make = \(\frac{2}{3}\) x 16

= 10.666 ≈ 10.67 mol of Fe

When we mix baking soda with lemon juice we can hear a hissing sound when bubbles of carbon di oxide coming out and rising is the reaction vessel.

The process of depositing a layer of zinc or chromium on iron is called Galvanisation.

The process of deposition of a layer of zinc on iron is called “Galvanization.”

1. When mango ripens, the contents present in the fruit gives good taste. The change in colour indicates that the fruit is ripend. 

2. Similar situations we experience with many fruits like banana, guava, papaya, pine apple … etc. 

3. In fact fruits are a gift to human beings as they give instantaneous energy when eaten. 

4. Nature is so kind to us to provide such ready made safe foods.

1.  If we observe that every change mentioned is the table repeats after some period of time. 

2. Such changes are known as periodic changes. 

3. The events which repeat at regular intervals of time are called periodic events.

The type of change that leads to the formation of a new substance is known as chemical change.

• During chemical change new substances are formed.
• Chemical composition of the substance changes.
• Heat, light may be Released or absorbed.
• A colour change may take place and sound may be produced.

Crystallization (Definition): 

The process of separating a soluble solid from the solution by heating or evaporating is called crystallization. 

Crystallization of copper sulphate: 

1. Take some hot, saturated solution of Copper sulphate in a test tube.

2. Pour some of it in an evaporating dish. 

3. Allow the solution to cool quickly. 

4. Observe with a magnifying glass, the size, colour and shape of the crystals formed.

Changes that occur with the formation of new substance with different chemical composition or transformation of a substance into another substance with the evolution or absorption of heat or light energy are termed as chemical changes.