Lenz law states that the direction of the induced e.m.f. is such as to oppose the cause of induction or the cause which produces.

According to Lewis’s concept, a covalent bond is formed when two atoms share a pair of electrons. For example, in a hydrogen molecule (H₂), each hydrogen atom shares its single electron with the other, forming a single covalent bond:

H⋅ + ⋅H → H − H

OR

The bond in sodium chloride (NaCl) cannot be expressed as Na-Cl because NaCl is an ionic compound, not a covalent one. Sodium (Na) donates an electron to chlorine (Cl), forming Na⁺ and Cl⁻ ions, which are held together by electrostatic forces rather than sharing electrons.

• Liquid covalent compound: Bromine (Br₂)
• Solid covalent compound: Diamond (a form of carbon)

When H₂S gas is passed through an aqueous copper sulfate (CuSO₄) solution, it reacts to form copper sulfide (CuS) and sulfuric acid (H₂SO₄). Balanced chemical equation:

CuSO₄​(aq) + H₂S(g) → CuS(s) + H₂SO₄ ​(aq)

When an aqueous solution of MSO₄ (where M is a metal) is electrolyzed, the cathode reaction is:

M²⁺(aq) + 2e⁻ → M (s)

Reason: This reaction is reduction because the metal cations (M²⁺) gain electrons (reduced) to form solid metal (M) at the cathode.

OR

Use of Copper:

• Electrical wiring – Copper is widely used for electrical wiring due to its excellent electrical conductivity.

Use of Aluminium:

• Aircraft construction – Aluminium is used in aircraft manufacturing because of its lightweight and high strength.

In the substitution reaction of methane with chlorine, the condition required is exposure to ultraviolet (UV) light or high temperatures. This initiates the reaction by generating chlorine radicals.

The balanced chemical equation for the first step (chlorination) is: CH₄ ​ + Cl₂ ​​ \overset \text{U V light} {\longrightarrow} CH₃Cl + HCl

OR

The balanced chemical equation for the reaction of ethanol with metallic sodium is:

2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂

In this reaction, ethanol (C₂H₅OH) reacts with sodium (Na) to form sodium ethoxide (C₂H₅ONa) and hydrogen gas (H₂).

The state of any gas can be completely be described by four variables such as pressure (P), Volume (V), Absolute temperature (T) and number of moles (n) of the gas.According to Boyle’s law:

V ∝ 1/P (T and n are constant)

According to Charle’s law:

V ∝ T (P and n are constant)

According to Avogadro’s law:

V ∝ n (P and T are constant)

By method of compound variation: V ∝ nT/p,

When P, T and n of the gas vary

Therefore, V ∝ RnT/P (R = molar gas constant).

Or, PV = nRT. This equation is called the Ideal Gas Equation.

Balanced Chemical Eq

4FeS₂ + 11O₂ → 2Fe₂O₃ + 8SO₂

480 g                                    512 g

From the equation, it is evident that 480 g of FeS₂ is required to produce 512 g of SO₂

OR

According to the law of conservation of mass, the mass of the gaseous compound produced = 200 - 112 = 88 g

Molecular weight (M) = 2 × VD

= 2 × 22

= 44 g

Number of moles (n) = 88/44 = 2

The thermal conductivity of a material is the amount of heat which when passes normally in one second through the opposite faces of unit cube (i.e, 1 m cube), the difference in temperature between its 2 opposite faces is 1⁰C. The S.I. unit of thermal conductivity is J.m^-1.K^-1.s^-1.

OR

The coefficient of linear expansion of a substance is the change in length relative to its original length at 0ºC per unit of temperature.
The S.I. unit of the coefficient of linear expansion of a substance is K^-1.

When the object is placed between focus and the optical centre, an erect and magnified image be formed with the help of a convex lens. Long Sightedness is rectified using a convex lens.

The R.I of a medium is given by,

μ  = Velocity of light in vacuum/Velocity of light in the medium

or, μ = 3 × 10^8\over 2 × 10^8

or, μ = 3\over2 = 1.5

OR

Refractive Index (μ) = sin\ i\over sin\ r

√2 = sin\ 45º\over sin\ r

sin r = sin\ 45º\over √2 

sin r = {1\over √2}\over √2

sin r = 1\over 2 = sin 30º

∠ r = 30º

Since refraction is taking place from rarer to denser medium,
angle of deviation,

δ = ∠ i - ∠ r  = 45⁰ - 30⁰ = 15⁰.

Joule’s law of heating :

If H amount of heat is produced in a conductor of resistance R, when a steady current I is passed through it for time t, then H is

1. directly proportional to the square of the current (H ∝ I²), when R and t are kept constant.
2. directly proportional to the resistance of the resistor (H ∝ R), when I and t are kept constant
3. directly proportional to the time for which the current flows through the resistor (H ∝ t), when I and R are kept constant.

Therefore, H = kI²Rt (k = Joule's constant)