Explanation Longitudinal Wave (Primary Nature): Sound propagates as compressions and rarefactions (particles vibrate parallel to wave direction). Example: Sound waves in air. Mechanical Wave (Medium Dependency): Requires a medium (solid, liquid, gas) to travel—cannot propagate in a vacuum. Transverse Wave (In Specific Cases): In solids, sound can also exhibit transverse wave components (particles vibrate perpendicular to the wave direction).

Explanation Active voice: " Did you catch the fly? " (past simple, interrogative) Passive voice: Start with " Was " (since " fly " is singular and past tense is used) " catch " → " caught " (past participle) Subject " you " comes after " by " Correct passive voice: Was the fly caught by you? Explanation Negative imperative sentence → passive voice starts with "Let... not be + past participle" " Do not pay " → "Let... not be paid" Object " him " becomes the subject in passive. Correct passive voice: Let him not be paid anything. Explanation Imperative sentence → passive voice starts with " Let " Base verb " strike off " → past participle is " struck off " Structure : Let + object + be + past participle Correct passive voice: Let his name be struck off. Explanation Tense : Future simple (will buy) Passive structure : will be + past participle " buy " → bought (past participle) Subject " he " → him Reflexive pronoun remains: for himself Correct passive voice: A ticket will be bought by him for himself. Explanation Tense : Present simple (They buy) Passive structure : Object + is/are + past participle + by + subject " Flowers " is plural → use " are " Past participle of buy is bought Correct passive voice: Beautiful flowers are bought by them. Explanation This is an interrogative sentence (yes/no question). " Did you see " → "I had seen" (past simple → past perfect) " my " → "her" " this room " → "that room" " said to " → "asked" We can use " if " or " whether " in indirect questions. So both are correct : She asked me whether I had seen her daughter in that room. She asked me if I had seen her daughter in that room. Explanation The sentence expresses a wish or prayer , so in indirect narration we use " prayed ". Changes: " May " → "might" " here " → "there" So, the correct indirect narration is: They prayed that train might reach there in time. Explanation This is a question sentence in indirect narration. Changes : " said to " → " asked " " were you sitting " → " they had been sitting " (past continuous → past perfect continuous) " here " → " there " So, the correct narration is: He asked them why they had been sitting there. Explanation Direct speech: " I broke my pencil today ." Changes in indirect speech: " I " → "she" " broke " (past) → "had broken" (past perfect) " my " → "her" " today " → "that day" So, the correct indirect narration is: She said to him that she had broken her pencil that day. Explanation Direct speech : " You are my best friend. " Indirect speech : Pronouns and tense change: " You " → " I " " are " (present) → " was " (past) " my " → " his " So the correct narration is: He said that I was his best friend.

Explanation Active voice: " Did you catch the fly? " (past simple, interrogative) Passive voice: Start with " Was " (since " fly " is singular and past tense is used) " catch " → " caught " (past participle) Subject " you " comes after " by " Correct passive voice: Was the fly caught by you? Explanation Negative imperative sentence → passive voice starts with "Let... not be + past participle" " Do not pay " → "Let... not be paid" Object " him " becomes the subject in passive. Correct passive voice: Let him not be paid anything. Explanation Imperative sentence → passive voice starts with " Let " Base verb " strike off " → past participle is " struck off " Structure : Let + object + be + past participle Correct passive voice: Let his name be struck off. Explanation Tense : Future simple (will buy) Passive structure : will be + past participle " buy " → bought (past participle) Subject " he " → him Reflexive pronoun remains: for himself Correct passive voice: A ticket will be bought by him for himself. Explanation Tense : Present simple (They buy) Passive structure : Object + is/are + past participle + by + subject " Flowers " is plural → use " are " Past participle of buy is bought Correct passive voice: Beautiful flowers are bought by them. Explanation This is an interrogative sentence (yes/no question). " Did you see " → "I had seen" (past simple → past perfect) " my " → "her" " this room " → "that room" " said to " → "asked" We can use " if " or " whether " in indirect questions. So both are correct : She asked me whether I had seen her daughter in that room. She asked me if I had seen her daughter in that room. Explanation The sentence expresses a wish or prayer , so in indirect narration we use " prayed ". Changes: " May " → "might" " here " → "there" So, the correct indirect narration is: They prayed that train might reach there in time. Explanation This is a question sentence in indirect narration. Changes : " said to " → " asked " " were you sitting " → " they had been sitting " (past continuous → past perfect continuous) " here " → " there " So, the correct narration is: He asked them why they had been sitting there. Explanation Direct speech: " I broke my pencil today ." Changes in indirect speech: " I " → "she" " broke " (past) → "had broken" (past perfect) " my " → "her" " today " → "that day" So, the correct indirect narration is: She said to him that she had broken her pencil that day. Explanation Direct speech : " You are my best friend. " Indirect speech : Pronouns and tense change: " You " → " I " " are " (present) → " was " (past) " my " → " his " So the correct narration is: He said that I was his best friend.

Explanation Active voice: " Did you catch the fly? " (past simple, interrogative) Passive voice: Start with " Was " (since " fly " is singular and past tense is used) " catch " → " caught " (past participle) Subject " you " comes after " by " Correct passive voice: Was the fly caught by you? Explanation Negative imperative sentence → passive voice starts with "Let... not be + past participle" " Do not pay " → "Let... not be paid" Object " him " becomes the subject in passive. Correct passive voice: Let him not be paid anything. Explanation Imperative sentence → passive voice starts with " Let " Base verb " strike off " → past participle is " struck off " Structure : Let + object + be + past participle Correct passive voice: Let his name be struck off. Explanation Tense : Future simple (will buy) Passive structure : will be + past participle " buy " → bought (past participle) Subject " he " → him Reflexive pronoun remains: for himself Correct passive voice: A ticket will be bought by him for himself. Explanation Tense : Present simple (They buy) Passive structure : Object + is/are + past participle + by + subject " Flowers " is plural → use " are " Past participle of buy is bought Correct passive voice: Beautiful flowers are bought by them. Explanation This is an interrogative sentence (yes/no question). " Did you see " → "I had seen" (past simple → past perfect) " my " → "her" " this room " → "that room" " said to " → "asked" We can use " if " or " whether " in indirect questions. So both are correct : She asked me whether I had seen her daughter in that room. She asked me if I had seen her daughter in that room. Explanation The sentence expresses a wish or prayer , so in indirect narration we use " prayed ". Changes: " May " → "might" " here " → "there" So, the correct indirect narration is: They prayed that train might reach there in time. Explanation This is a question sentence in indirect narration. Changes : " said to " → " asked " " were you sitting " → " they had been sitting " (past continuous → past perfect continuous) " here " → " there " So, the correct narration is: He asked them why they had been sitting there. Explanation Direct speech: " I broke my pencil today ." Changes in indirect speech: " I " → "she" " broke " (past) → "had broken" (past perfect) " my " → "her" " today " → "that day" So, the correct indirect narration is: She said to him that she had broken her pencil that day. Explanation Direct speech : " You are my best friend. " Indirect speech : Pronouns and tense change: " You " → " I " " are " (present) → " was " (past) " my " → " his " So the correct narration is: He said that I was his best friend.

Explanation Active voice: " Did you catch the fly? " (past simple, interrogative) Passive voice: Start with " Was " (since " fly " is singular and past tense is used) " catch " → " caught " (past participle) Subject " you " comes after " by " Correct passive voice: Was the fly caught by you? Explanation Negative imperative sentence → passive voice starts with "Let... not be + past participle" " Do not pay " → "Let... not be paid" Object " him " becomes the subject in passive. Correct passive voice: Let him not be paid anything. Explanation Imperative sentence → passive voice starts with " Let " Base verb " strike off " → past participle is " struck off " Structure : Let + object + be + past participle Correct passive voice: Let his name be struck off. Explanation Tense : Future simple (will buy) Passive structure : will be + past participle " buy " → bought (past participle) Subject " he " → him Reflexive pronoun remains: for himself Correct passive voice: A ticket will be bought by him for himself. Explanation Tense : Present simple (They buy) Passive structure : Object + is/are + past participle + by + subject " Flowers " is plural → use " are " Past participle of buy is bought Correct passive voice: Beautiful flowers are bought by them. Explanation This is an interrogative sentence (yes/no question). " Did you see " → "I had seen" (past simple → past perfect) " my " → "her" " this room " → "that room" " said to " → "asked" We can use " if " or " whether " in indirect questions. So both are correct : She asked me whether I had seen her daughter in that room. She asked me if I had seen her daughter in that room. Explanation The sentence expresses a wish or prayer , so in indirect narration we use " prayed ". Changes: " May " → "might" " here " → "there" So, the correct indirect narration is: They prayed that train might reach there in time. Explanation This is a question sentence in indirect narration. Changes : " said to " → " asked " " were you sitting " → " they had been sitting " (past continuous → past perfect continuous) " here " → " there " So, the correct narration is: He asked them why they had been sitting there. Explanation Direct speech: " I broke my pencil today ." Changes in indirect speech: " I " → "she" " broke " (past) → "had broken" (past perfect) " my " → "her" " today " → "that day" So, the correct indirect narration is: She said to him that she had broken her pencil that day. Explanation Direct speech : " You are my best friend. " Indirect speech : Pronouns and tense change: " You " → " I " " are " (present) → " was " (past) " my " → " his " So the correct narration is: He said that I was his best friend.

Explanation Active voice: " Did you catch the fly? " (past simple, interrogative) Passive voice: Start with " Was " (since " fly " is singular and past tense is used) " catch " → " caught " (past participle) Subject " you " comes after " by " Correct passive voice: Was the fly caught by you?

Explanation The hertz is the unit of frequency  of one cycle per second.   symbol: hertz (Hz) Hertz in honor of the German physicist Heinrich Hertz hertz in the International System of Units (SI) frequency i s defined as one cycle per second *** Explanation Exponential notation (scientific notation) is used to express very small (e.g., 0.0000001) or very large (e.g., 1000000000) quantities compactly by representing numbers as powers of 10 . Key Information : Format : a × 10^n, where 1 ≤ a < 10 and n is an integer. Used for very large or very small numbers . Examples: Large number : 6.022 × 10^23 ( Avogadro's number ) Small number : 1.6 × 10^-19 ( Charge of an electron ) Explanation Marconi  invented  Radio . Radio was invented in  1895 . Guglielmo Marconi was an  Italian  inventor.  ***** Explanation The Mole (mol) is the SI unit of amount of substance, representing 6.022 x 10^23 particles. It is used to measure the amount of a substance in a sample. Explanation Louis Pasteur (1822–1895) was a pioneering microbiologist and chemist whose work bridged both fields: As a Chemist : Discovered molecular chirality (optical isomers). Studied fermentation, proving it was caused by microorganisms. As a Microbiologist : Developed pasteurization (heat treatment to kill microbes in food). Created vaccines for rabies and anthrax. Disproved spontaneous generation (germ theory of disease). Explanation The chemical formula CH₃COOH represents acetic acid , a weak organic acid commonly found in vinegar. Key Information : Common Name : Acetic acid (systematic name: ethanoic acid). Properties : Weak acid (partially dissociates in water). Pungent smell, sour taste (vinegar contains ~4–8% acetic acid). Explanation Xylem and Phloem are specialized conducting tissues in vascular plants: Xylem : Transports water and minerals from roots to other parts (unidirectional). Phloem : Transports sugars (photosynthates) from leaves to other parts (bidirectional). Explanation The atomic weight of Mercury (Hg) is 200.59 unified atomic mass units (u), as listed on the periodic table. Key Information : Symbol : Hg (from Latin Hydrargyrum) Atomic Number : 80 Standard Atomic Weight : 200.592 u (often rounded to 200.59 u). Explanation The mass of Earth is approximately 6.0 x 10^24 kilograms ( 5.98 x 10^24 kg ). This is a widely accepted scientific value , based on various measurements and calculations, including: Gravity measurements Satellite orbits Seismological data Planetary formation models Explanation Longitudinal Wave (Primary Nature): Sound propagates as compressions and rarefactions (particles vibrate parallel to wave direction). Example: Sound waves in air. Mechanical Wave (Medium Dependency): Requires a medium (solid, liquid, gas) to travel—cannot propagate in a vacuum. Transverse Wave (In Specific Cases): In solids, sound can also exhibit transverse wave components (particles vibrate perpendicular to the wave direction).

Explanation Negative imperative sentence → passive voice starts with "Let... not be + past participle" " Do not pay " → "Let... not be paid" Object " him " becomes the subject in passive. Correct passive voice: Let him not be paid anything.

Explanation The hertz is the unit of frequency  of one cycle per second.   symbol: hertz (Hz) Hertz in honor of the German physicist Heinrich Hertz hertz in the International System of Units (SI) frequency i s defined as one cycle per second ***

Explanation Imperative sentence → passive voice starts with " Let " Base verb " strike off " → past participle is " struck off " Structure : Let + object + be + past participle Correct passive voice: Let his name be struck off.