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The correct answer is Ethene

Concept:-

• Elimination reactions: In organic chemistry, an elimination reaction is a reaction in which one molecule is broken down into two smaller molecules, with the 'elimination' of a small molecule such as water.
• Dehydration reactions: Dehydration is a specific type of elimination reaction that involves the loss of a water molecule during the reaction. The name "dehydration reaction" literally describes what happens - a molecule is dehydrated, or loses water.

Explanation:-

When ethanol is heated with sulfuric acid, the major product is ethene (option 2).

The reaction is a dehydration reaction, which means it involves the removal of a water molecule (H₂O). In this case, ethanol (C₂H₅OH) heated with sulfuric acid (H₂SO₄, which acts as a catalyst) results in the production of ethene (C₂H₄) plus water (H₂O).

The overall reaction can be written as follows:

C₂H₅OH → C₂H₄ + H₂O

So, the correct answer is Ethene.

CONCEPT:

Molecular Formula of Saturated Hydrocarbons (Alkanes)

• Saturated hydrocarbons are known as alkanes.
• They follow the general molecular formula: C_nH_2n+2
• In a saturated hydrocarbon (no double or triple bonds), each carbon is bonded with four atoms using single bonds only.

EXPLANATION:

• Given that the hydrocarbon is classified as an octane, it contains 8 carbon atoms → n = 8
• Using the general formula:
• C_nH_2n+2 → C₈H_2×8+2 = C₈H₁₈
• This corresponds to a fully saturated molecule of octane.
• Other options:
• C₈H₈: Too few hydrogens — likely an unsaturated or aromatic compound.
• C₈H₁₄ and C₈H₁₆: Also unsaturated (alkenes or cycloalkanes).

Therefore, the correct answer is Option 4) C₈H₁₈, which is the molecular formula of octane, a saturated hydrocarbon.

CONCEPT:

Stoichiometry and Percentage Composition

• To solve this problem, we use the concept of percentage composition to determine how much oxygen is present in a given amount of magnesium carbonate (MgCO₃).
• Molecular mass of MgCO₃ = 84.3 g/mol
• It contains:
• Mg = 24.3 g/mol
• C = 12.0 g/mol
• O = 3 × 16.0 = 48.0 g/mol
• So, in 84.3 g of MgCO₃, there are 48.0 g of oxygen.

EXPLANATION:

• We use a unitary method:

If 48.0 g O is in 84.3 g MgCO₃,

Then 24.0 g O is in: 

\( \dfrac{84.3 \times 24.0}{48.0} \)

= 42.15 g ≈ 42.2 g

Therefore, the correct answer is Option 1) 42.2 g.

Concept:

• To hear a distinct echo, the time interval between the original sound and reflected sound must be at least 0.1 seconds.
• The sensation of sound persists in our brain for about 0.1 seconds.
• If we take the speed of sound to be 344 minutes per second at a given temperature, suppose at 22-degree celsius in the air, the sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1 seconds.

Additional Information

• The original sound persists in our ear for 0.1 s.
• So to hear an echo, the reflected sound must be reaching our ears at least after 0.1 s.
• Assuming the speed of sound in air as 340 m/s, we can calculate the distance travelled by the sound

⇒ D = speed × time = 340 x 0.1 = 34 m.

• This 34 m is the combined to and fro distance from the source to the reflected surface.

So, one way distance = 34/2 = 17 m.

• Hence, 17 m is the minimum distance required between the reflecting surface and source to hear an echo.

CONCEPT:

Colloids and Their Characteristics

• A colloid is a heterogeneous mixture where the particle size ranges between 1 nm and 1000 nm.
• Colloids appear homogeneous to the naked eye but are heterogeneous microscopically.
• They show the Tyndall effect and do not settle on standing.
• Common types include emulsions (like milk), gels (like butter), sols (like mud), etc.

EXPLANATION:

• Milk:
• An emulsion (liquid in liquid type colloid).
• Colloid
• Mud:
• An example of a sol (solid in liquid type colloid).
• Colloid
• Butter:
• A gel (liquid dispersed in solid).
• Colloid
• Boric Acid:
• A pure compound or solution when dissolved in water.
• Does not form a colloid on its own.
• Not a colloid

Therefore, the correct answer is Option 4) Boric acid.

CONCEPT:

Nature and Behavior of Sound Waves

• Sound waves are mechanical longitudinal waves, meaning particles oscillate parallel to the direction of wave propagation.
• Sound waves can exhibit various wave phenomena such as:
• Reflection: Bouncing back of sound from a surface.
• Diffraction: Bending of sound waves around obstacles.
• Interference: Combination of two or more sound waves to form a resultant wave.
• Polarization is a property of transverse waves, where oscillations occur perpendicular to the direction of wave motion.
• Since sound waves are longitudinal, they cannot be polarized.

EXPLANATION:

• Diffraction: Occurs in sound waves.
• Reflection:  Occurs in sound waves (used in echo, sonar).
• Polarization:  Does NOT occur in sound waves (as they are longitudinal).
• Interference:  Occurs in sound waves (constructive and destructive interference).

Therefore, the correct answer is Option 3) Polarization.

Concept:

Potential energy, is stored energy that depends upon the relative position of various parts of a system.

Calculation:

Potential energy is constant

mgh_e = m \({g \over 6}\)h_m

where,h_e​ = height on earth,h_m = height on moon)

h_m = 6h_e

​

 =6×10

= 60m

Hence, he can jump 60m high on the moon.

The correct answer is option (2).

The correct answer is Only (A) and (B) of the above.

Explanation:

• Greenhouse gases are responsible for the greenhouse effect. These gases absorb and emit energy within the thermal infrared range.
• Greenhouse gases are gases in Earth's atmosphere that trap heat. They let sunlight in but prevent some of the heat that the sunlight brings from leaving the atmosphere.
• Common greenhouse gases include water vapour, carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and ozone.
• Water vapour (A): It is the most abundant greenhouse gas in the atmosphere. It increases in concentration as the Earth's atmosphere warms, amplifying the greenhouse effect.
• Ozone (B): Ozone in the lower atmosphere (troposphere) acts as a greenhouse gas, trapping heat and contributing to the greenhouse effect. However, stratospheric ozone protects life on Earth by blocking harmful ultraviolet radiation from the sun.
• Carbon monoxide (C): While carbon monoxide itself is not a significant greenhouse gas, it can indirectly influence climate. It reacts with other compounds in the atmosphere to form carbon dioxide and ozone, both of which are greenhouse gases.
• Nitrogen (D): Nitrogen is the most abundant gas in the Earth's atmosphere but it is not a greenhouse gas.

Key Points

• Algae are chlorophyll-bearing, simple, thalloid, autotrophic, and predominantly aquatic organisms.
• They occur in various habitats ranging from oceans, rivers, and lakes to ponds, brackish waters to most stones, woods, moist soil, and snow.
• The form and size of algae are highly variable, some are microscopic unicellular, some are colonial, some are filamentous, and some have massive plant bodies.
• Algae are polyphyletic, as these organisms do not share a common ancestor and are not related to each other.
• They lack a well-defined body and do not possess structures like roots, stems, or leaves.
• There are different classes of algae are -

1. Chlorophyceae - 

• The members of Chlorophyceae are commonly called green algae.
• They are green due to the dominance of pigments chlorophyll a and b.​

2. Phaeophyceae - 

• The members of Phaeophyceae known as brown algae are primarily found in marine habitats.
• They possess chlorophyll a, c, carotenoids, and xanthophylls mainly fucoxanthin.

3. Rhodophyceae - 

• The members of Rhodophyceae are commonly known as red algae because of the predominance of the red pigment, **r-phycoerythrin in their bodies.
• Red algae also contain chlorophyll a and d.

Explanation:

• Sphagnum is a genus of mosses belonging to the Bryophytes.
• It is commonly known as peat moss or bog moss.
• It is found in wet and boggy areas and requires acidic soil to grow.
• Bryophytes are the first land- inhabiting, embryophytes, and archegoniate without vascular bundles.
• Bryophytes include the various mosses and liverworts that are found commonly growing in moist shaded areas.
• These are also called amphibians of the plant kingdom as these plants can live in soil but are dependent on water for sexual reproduction.
• The main plant body of Sphagnum is called gametophyte.
• The gametophyte is differentiated into a main axis with branches and leaves.
• They possess root-like structures called rhizoids.
• Sphagnum shows an alternation of generation with the dominant haploid gametophytic stage.
• The species of Sphagnum can reproduce either unisexually or bisexually.
• The sexual reproduction in Sphagnum is of advanced oogamous type.
• Species of Sphagnum provide peat that has long been used as fuel and as packing material for the trans-shipment of living materials due to their water-holding capacity.

Additional InformationFucus-

• It is a genus of brown alga found in intertidal and shallow water bodies.
• It is a dioecious and multicellular alga.
• The plant body is generally attached to the substratum by holdfast and has a stalk, stipe, and leaf-like photosynthetic structure called the frond.

Porphyra-

• It is a genus of the class Rhodophyceae.
• The coldwater seaweeds grow in shallow seawater.
• It exhibits a heteromorphic alternation of generations.
• Porphyra is an edible seaweed and a source of vitamin B12.

Polysiphonia-

• Polysiphonia is a genus of filamentous red alga.
• They are exclusively marine.
• The thallus consists of fine-branched filaments that are attached to the main axis.

Hence, the correct answer is Sphagnum.

Key Points

• Algin is a mucopolysaccharide found in the cell walls of algae.
• It is a linear copolymer that is composed of residues D-mannuronic acid and L-glucuronic acid.
• In Phaeophytes, the cell wall consists of cellulose and Algin.
• The gelatinous coating of Algin covers the cellulosic wall of the vegetative cells on the outside.
• The members of Phaeophyceae known as brown algae are primarily found in marine habitats.
• They possess chlorophyll a, c, carotenoids, and xanthophylls mainly fucoxanthin.
• The food is stored as complex carbohydrates in Phaecophytes, which may be in the form of laminarin or mannitol.
• The plant body of Phaecophytes is divided into three parts- the attachment organ holdfast, the stalk stipe, and the leaf-like photosynthetic organ- the frond.
• For e.g., Ectocarpus, Fucus, Sargassum, Laminaria, etc.

Additional InformationRhodophytes-

• Rhodophytes are commonly known as red algae because of the predominance of the red pigment, r-phycoerythrin in their bodies.
• Red algae also contain chlorophyll a and d.
• The majority of the red algae are marine with greater concentrations found in the warmer regions.
• The cell wall is made up of cellulose, pectin, and polysulphate esters.

Pteridophytes-

• Pteridophytes are the first terrestrial plants that possess vascular tissues - xylem and phloem.
• These are found in cool, damp, shady areas, some species may also flourish in sandy-soil conditions.
• In Pteridophytes, the main plant body is sporophytes that differentiated into true roots, stems, and leaves.
• Pteridophytes are further classified into four classes, namely Psilopsida, Lycopsida, Sphenopsida, and Pteropsida.

Gymnosperms-

• Gymnosperms are plants in which the ovules are not enclosed by any ovary wall and remain exposed both before and after fertilization.
• Gymnosperms include medium-sized trees or tall trees and shrubs.
• The roots are generally tap roots and the leaves are well-adapted to withstand extremes of temperature, humidity, and wind.
• The gymnosperms are heterosporous, they produce haploid microspores and megaspores.

Hence, the correct option is (1) Phaeophytes.