Matter

Intermolecular force of attraction decreases; kinetic energy increases, Intermolecular force of attraction remains the same; kinetic energy increases

Step 1: When a solid is heated, energy is supplied to its particles. Step 2: This supplied energy converts into kinetic energy of the particles, making them vibrate faster and then move more freely. Step 3: As kinetic energy increases, the particles can overcome the intermolecular forces of attraction holding them together. Step 4: As a result, intermolecular forces DECREASE while kinetic energy INCREASES. Step 5: Option A is wrong because forces do not increase on heating. Option C is wrong because kinetic energy never decreases on heating. Option D is wrong because forces do change — they de

Water molecules collide with pollen grains from all directions with unequal forces at any given moment

Step 1: Brownian motion is the random, zig-zag movement of suspended particles caused by the collision of moving liquid (or gas) molecules with those particles. Step 2: Water molecules are in constant random motion and collide with pollen grains continuously. Step 3: At any instant, collisions happen from all sides, but the number and force of collisions from different directions are NOT equal. Step 4: This unequal bombardment pushes the pollen grain in one direction, then another, creating the zig-zag path. Step 5: Option A is wrong — pollen grains used in Robert Brown's experiment were dead.

High pressure and low temperature

Step 1: To convert a gas into a liquid, we need to bring its particles closer together. Step 2: Increasing pressure forces gas molecules closer to each other, reducing intermolecular space and increasing intermolecular forces of attraction. Step 3: Decreasing temperature reduces the kinetic energy of gas molecules, making it easier for intermolecular forces to hold them together in liquid form. Step 4: Both conditions together — HIGH pressure and LOW temperature — are used to liquefy gases like LPG, oxygen, and hydrogen. Step 5: High temperature (Option A and D) increases kinetic energy, which

To prevent carbon dioxide gas (a product) from escaping, which would make the measured mass of products less than reactants

Step 1: The reaction is: NaHCO₃ + CH₃COOH → CO₂ + CH₃COONa + H₂O. Step 2: CO₂ is a gas and a product of this reaction. Step 3: If the bag is not sealed, CO₂ gas escapes into the atmosphere. Step 4: When we weigh after the reaction, the mass of escaped CO₂ will not be counted, making it appear that mass was lost — falsely suggesting the law of conservation of mass is violated. Step 5: To correctly verify the law, ALL products must remain within the closed system. Option A is incorrect — vinegar evaporation is negligible and not the main concern. Option C is wrong — pressure plays no role here.