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Bohr’s model of an atom: Electrons are present in stationary states. The electron moves to a higher energy level If it absorbs energy in the form of electromagnetic energy or moves to a lower energy state by emitting energy in the form of electromagnetic energy of appropriate frequency.

Electrons in an atom can gain energy by absorbing a particular frequency of light and can lose energy by emitting a particular frequency of light.

Electromagnetic energy (light) can have only certain discrete energy values which are given by the equation E = hv.

Since, Atomic number = Number of protons = Number of electrons

Therefore,

Atomic number of sodium = 11

Number of electrons in sodium = 11

The second shell has the capacity of 8 electrons.

James Chadwick discovered neutron.

The electric force might be acting in the atomic structure. In the atomic structure, electric force is much stronger than gravitational force. 

[Note: Here the gravitational force is very very small compared to the electric force, therefore, the gravitational force can be ignored.]

1. SRY – Sex Determining region 

2. TDF – Testes Determining Factor

Liquefaction of Gases : A gas can be liquefied by decreasing the temperature or by increasing the pressure or by the combination of both.

Data : n_{i + 1} – n_i = Y, n₁₂ = 2n₁ , n₅ = 90 Hz n₂ – n₁ = Y beats/s

∴ n₂ = n₁ + Y beats/s

Similarly, n₃ = n₂ + Y = n₁+ Y + Y

∴ n₃ = n₁ + 2Y = n₁ + (3 – 1) Y

∴ n_x = n₁ + (x – 1) Y

Similarly, n₁₂ = n₁ + (12 – 1) Y = n₁ + 11Y

∴ n₁₂ = 2n₁ = n₁ + 11Y

∴ n₁ = 11Y

Also, n₅ = n₁ + (5 – 1) Y = n₁ + 4Y

∴ n₅ = 11Y + 4Y = 15Y

∵ n₅ = 90 Hz 

∴ 15Y = 90 

∴ Y = 6

∴ n₁ = 11Y beats/s = 11 × 6 beats/s = 66 Hz 

and n₁₂ = 2n₁ = 2 (66) = 132 Hz

True

The elements having one valency are called monovalent. The given statement is correct.

Every cell would have three features- plasma membrane, nucleus and cytoplasm. All activities inside the cell and interactions of the cell with its environment are possible due to these features.

False

A group of atoms carrying a charge is called polyatomic ion. These are a group of atoms carrying either a negative or positive charge. For example: SO₃^2-, OH^- etc.

Hence, the given statement is wrong.

All living organisms are made up of cells. Cell is the basic structural and functional unit of complex organisms

➢ Atom is the smallest particle of an element. It has two parts: nucleus and outer nuclear part.

➢ Nucleus of the atom consists of protons and neutrons. Protons are positively charged particles. Neutrons possess no charge.

➢ In outer nuclear part, electrons are present. Electrons are negatively charged particles.

➢ Atomic number represents the number of protons in an atom. As atoms are electrically neutral, an atom contains as many electrons as it has protons. The total number of protons and neutrons present in one atom of an element is known as its mass number.

➢ The arrangement of electrons in the various shells/orbits/energy levels of an atom of the element is known as electronic configuration.

➢ Atoms of a given atomic number can have different number of neutrons are called isotopes.

➢ The atoms of different elements, which have the same mass number but different atomic numbers are called isobars. These have different number of protons but equal sum of number of protons and neutrons.

➢ The atoms of different elements, which have the same number of neutrons but different atomic numbers, are called isotones.

John Dalton (1803) stated this law as 'when two elements combine with each other to form two or more than two compounds, the mass of the element which combine with the fixed mass of the other bears a simple whole number ratio'.

After crossing the first gulf/ditch, the travellers travelled some distance and came across another gulf which was broader and deeper than the first ditch/gulf. It was impossible for the lion to jump across. The Scarecrow came up with an idea. He asked Tin Woodman to chop the tree near the ditch, in such a way that it fell across the gulf creating a bridge. The travellers successfully crossed this gulf too.

No, it is only a mathematical concept.

The centre of mass of a system consisting of a large number of particles is a point in the system, where if all the mass of the system were to be concentrated at the nature of motion executed by the system remains unaltered, when the external forces acting on the system are applied directly at this point.

A rigid body is that in which the distances between all its constituent particles remain fixed under the application of an external force.

Scalar: Volume, mass, speed, density, number of moles, angular frequency
Vector: Acceleration, velocity, displacement, angular velocity
 

A scalar quantity is specified by its magnitude only. It does not have any direction associated with it. Volume, mass, speed, density, number of moles, and angular frequency are some of the scalar physical quantities. 

A vector quantity is specified by its magnitude as well as the direction associated with it. Acceleration, velocity, displacement, and angular velocity belong to this category.

1. a. Convex lens

2. c. Real and inverted

3. a. Positive

4. d. Focus

5. b. 20 cm

1. c. Atmospheric refraction

2. b. Towards the normal

3. b. Law of refraction

4. a. TRUE

5. b. Refraction

(a) Thick 

(b) Thin

(a^b + b^a )^-1 

= (2³ + 3² )^-1 

= (2 × 2 × 2 × 3 × 3)^-1 

= (8 + 9)^-1 

= (17)^-1

= 1/17

False.

The value of (2⁰ + 3⁰ ) x 4⁰ is equal to 2.

2^a/b = 2⁰

2^a/b = 1

a/b = 0

∴ a = 0 

Base are same so power will be equal.

True

Value of (9/8)^-3 x (8/9)^-3 is equal to 8/9.

The exponential form of (2/5 x 2/5 x 2/5) x (3/5 x 3/5) is (2/5)³ x (3/5)².

The exponential form of 5/6 x 5/6 x 5/6 x 5/6 is (5/6)⁴.

729 

= 3 × 3 × 3 × 3 × 3 × 3 

= (3)⁶

Exponential form 3/4 x 3/4 x 3/4 of is (3/4)^3.

If a is a non zero rational number and n is a positive integer then a^-n = 1/aⁿ.

A number is called standard in form if it is expressed in K x 10ⁿ , n = an integer.

In (4/5)⁵⁰, then power is 50 and base is 4/5.

The power in (-8/3)²⁴ is 24.

2¹⁰ = 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2

5⁵ = 5 x 5 x 5 x 5 x 5 .

The correct option is (b) 4.

Simplest form of (2 x 4)² is 2² x 4².

Form of Exponent in (4)⁹ x (4)³ is (4)¹².

The value of (3⁵ x 3³ ) ÷ (3)¹⁴ is 1/3⁶.

The value of (-1)¹⁰¹ equal to -1.

(b) 2⁰ × 3⁰ × 4⁰

For any non-zero integers ‘a’ and ‘b’ and whole numbers m and n,

a⁰ = 1

So, 2⁰ = 1, 3⁰ = 1, 4^o = 1

Then, (1 × 1 × 1)

= 1

(d) 2⁴/(7⁰ + 3⁰)³

= 2⁴/(1 + 1)³

= 2⁴/2³

(c) -1/64

Cube of (-1/4) is = -1³/4³

= (-1 × -1 × -1)/(4 × 4 × 4)

= -1/64

Correct option is (D) a^-7

\(a^3\times a^{-10}=a^{3+(-10)}\) \(=a^{3-10}=a^{-7}\)

Correct option is  D) a^-7

(4)^2x+1 ÷ 16 = 64 

(4)^2x+1 ÷ 16 = 64 

or, (4)^2x+1 ÷ (4)² = 64 

or, 4^2x+1-2 = 4³ 

or, 4^2x-1= 4³ 

Comparing the exponents of same bases in both sides 

∴ 2x – 1 = 3 

or, 2x = 3 + 1 = 4 

or, x = 4/2 = 2

(b) z^-6

(By the law of exponents: (a^m)ⁿ=a^mn)

Correct option is (D) 1

\((xy)^{-2}.(xy)^2=(xy)^{-2+2}=(xy)^0=1\)

Correct option is  D) 1