RRB Group D 2025 Shift 3 Official Paper — Kerala PSC PYQ Practice with Answers

Correct answer (Option C):\nThis phenomenon is a direct application of Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. When the gun exerts a force forward on the bullet (action), the bullet exerts an equal and opposite force backward on the gun (reaction). This backward force causes the recoil of the gun.\n\nWhy others are wrong:\nOption A is wrong because the barrel does exert a powerful forward force on the bullet via expanding gas. Option B is wrong because air resistance opposes forward motion and acts backward. Option D is incorrect because gravity acts downward, not forward.\n\nStudy tip:\nRemember Newton's third law pairs always act on two different bodies. Here, the action is on the bullet, and the reaction is on the gun.

Correct answer (Option D):\nLiquids are a state of matter characterized by weak intermolecular forces compared to solids, allowing their particles to slide past one another and assume the shape of whatever vessel holds them. However, these forces are strong enough to keep the particles close together, preserving a fixed volume regardless of the container's configuration.\n\nWhy others are wrong:\nOption A describes the property of gases, which have neither definite volume nor definite shape. Option B illustrates solids, which possess both a fixed shape and volume. Option C describes an elastic solid containing trapped air pockets, not liquid behavior.\n\nStudy tip:\nKinetic molecular theory states that liquids have closely packed particles that can move freely, explaining why volume stays constant while shape easily adapts.

Correct answer (Option D):\nGalvanisation is a metallurgical process where iron or steel is coated with a thin protective layer of zinc. Zinc acts as a sacrificial anode because it is more reactive than iron; it corrodes preferentially, thereby shielding the underlying iron structure from atmospheric oxygen and moisture to prevent rust formation.\n\nWhy others are wrong:\nOption A involves treating a metal surface to reduce chemical reactivity, usually forming an oxide layer, not adding zinc. Option B is a broader technique to control corrosion by making the metal a cathode, often using a sacrificial metal but not specifically coating it entirely. Option C is generic electrical deposition of any metal.\n\nStudy tip:\nZinc protects iron even if the coating is scratched because its higher standard reduction potential ensures it oxidizes before the iron does.

Correct answer (Option D):\nSaturated organic compounds are hydrocarbons or their derivatives where all carbon-to-carbon bonds are single covalent bonds. Bromopropane contains only single C-C bonds, meaning every carbon atom is fully bonded with the maximum number of single links. This suffix '-ane' denotes a saturated alkane framework.\n\nWhy others are wrong:\nOption A and Option B contain 'propene', which contains a carbon-carbon double bond, making them unsaturated. Option C contains 'propyne', which features a carbon-carbon triple bond, also making it unsaturated.\n\nStudy tip:\nLook at the suffixes: '-ane' implies saturated (alkanes), while '-ene' (alkenes) and '-yne' (alkynes) signify unsaturated structures with multiple bonds.

Correct answer (Option C):\nButane is a normal alkane (n-butane) consisting of four carbon atoms bonded together in a continuous, unbranched linear layout: CH₃-CH₂-CH₂-CH₃. Straight-chain hydrocarbons contain no side branches emerging from the main skeletal track.\n\nWhy others are wrong:\nOption A has a methyl branch at the third carbon. Option B possesses a methyl branch on a three-carbon chain. Option D is the common name for 2-methylpropane, which is a branched isomer of butane.\n\nStudy tip:\nPrefixes like 'iso-' or names containing numbers indicating side groups (like methyl) signal branched-chain hydrocarbons, whereas plain standard alkanes like butane are straight-chained.