Free Scientific Reasoning MCQs with Answers

231. A supermarket offers delivery to the customer's house, but makes a charge for the service. The charge is 10% of the cost of the items purchased, plus an extra $1 if any of the items needs to be kept chilled. An additional $3 is added on to the charge if the delivery is over a distance of more than 10km.Jeremy has had his shopping delivered to his house. The delivery cost was $6.40.What is the lowest possible total cost of Jeremy's items?

• A. $24
• B. $34
• C. $60
• D. $64

Explanation: To determine the lowest possible total cost of Jeremy's items, we start by analyzing the delivery charge of $6.40. The charge includes 10% of the cost of the items, plus $1 if any item needs to be chilled, and an additional $3 if the delivery distance is over 10km. The minimal configuration for these charges is a $1 chilled item fee and the 10% charge on the cost of items, totaling $4.40 ($6.40 - $1 - $3). This implies the 10% charge accounts for $3.40 of the delivery fee, meaning the cost of the items is $34 ($3.40 / 0.10). Therefore, the lowest possible total cost is $34. Option A suggests a lower item cost, which is inconsistent with the delivery fee constraints. Options C and D assume unnecessarily high item costs, which would result in a delivery fee exceeding $6.40.

232. Experiment: A blue copper sulfate solution was electrolyzed using copper electrodes.Observation: The color of the solution remained unchanged, and copper deposited on the cathode.Question: What does this indicate?

• A. Electrolysis converts copper to zinc
• B. No ion exchange occurs during electrolysis.
• C. Copper ions are transferred but concentration stays constant.
• D. Color change must occur in redox reactions

Explanation: This process is the transfer of copper from one electrode to the other.Anode (+): Copper dissolves into the solution: 𝐶u→𝐶u(𝑔)+2𝑒−, so it loses mass. Cathode (-): Copper ions deposit onto the electrode Cu²⁺+2e⁻→Cu(s), so it gains massBecause copper ions are replaced as quickly as they are removed, the concentration stays constant and the blue color does not fade. Hence, Option C is correct.

233. Experiment: Dilute hydrochloric acid was added to marble chips in a conical flask connected to a gas syringe.Observation: Gas volume increased with time until it plateaued.Question: What can be concluded?

• A. Marble turns into gas over time
• B. Gas leaks caused the stop in reaction.
• C. Reaction rate decreases as reactants are used up.
• D. Acid stopped boiling due to temperature drop.

Explanation: The correct answer is C, because as the chemical reaction proceeds, the particles of the reactants (marble chips and acid) are used up to form the products.Initial Stage: There are a large number of particles of the reactants, and hence the collision frequency is high, and the gas evolves readily.Middle Phase: The concentration of the acid and the surface area of the marble are decreasing because the reactants are being consumed. This causes the collisions to slow down, leading to a decrease in the rate of reaction.The Plateau: The volume of gas evolved ceases to rise (plateaus) because a gas has reacted completely, meaning that this particular chemical reaction is complete.

234. Experiment: A mixture of iron filings and sulfur was heated strongly in a test tube.Observation: A black solid formed that was attracted by a magnet only slightly.Question: What does this demonstrate?

• A. Iron underwent a chemical change to form a new compound with sulfur.
• B. A compound (iron sulfide) was formed with unique properties.
• C. The mixture remained unchanged despite heating.
• D. Iron reacted with sulfur to form a new substance, not rust.

Explanation: The correct answer is Option B: A compound (iron sulfide) was formed with unique properties. This demonstrates a chemical reaction where iron and sulfur combined to create a new compound, iron sulfide, distinguished by its distinct properties. Option A is incorrect as it describes a physical change, not a chemical one. Option C is inaccurate as a new substance was indeed formed. Option D is incorrect because rust formation involves iron reacting with oxygen, not sulfur.

235. Experiment: A beaker containing water and ice was kept at room temperature and its temperature was recorded every minute.Observation: The temperature remained at 0°C until all ice melted.Question: What does this show?

• A. Ice absorbs no heat from the surroundings.
• B. Melting lowers temperature further.
• C. Water is a poor conductor of heat.
• D. Latent heat of fusion keeps temperature constant during phase change.

Explanation: The correct answer is Option D: Latent heat of fusion keeps temperature constant during phase change. This explanation is supported by the observation that the temperature remained constant at 0°C until all ice melted. The latent heat of fusion is the energy required to change a substance from solid to liquid, and during this phase change, the absorbed heat is used to break the intermolecular bonds rather than increase the temperature. The other options are incorrect because they do not accurately explain the phenomenon observed in the experiment.

236. Experiment: Aluminium foil was added to a solution of dilute sulfuric acid.Observation: Bubbles of gas formed and the foil slowly dissolved.Question: Which gas is being evolved?

• A. Hydrogen, due to reaction of metal with acid.
• B. Oxygen, from aluminum breakdown.
• C. Nitrogen, from sulfuric acid.
• D. Carbon dioxide, from aluminum oxide.

Explanation: The correct answer is Option A: Hydrogen, due to the reaction of the metal with the acid. When aluminium reacts with sulfuric acid, hydrogen gas is evolved. This is a common observation in such reactions. Options B, C, and D are incorrect as oxygen, nitrogen, and carbon dioxide are not the gases typically evolved when aluminium reacts with sulfuric acid.

237. Experiment: A burning candle was placed in a closed bell jar.Observation: The flame extinguished after some time and condensation appeared inside the jar.Question: What conclusion can be made?

• A. Carbon dioxide supports combustion.
• B. Oxygen is necessary for combustion and is used up.
• C. Water is released from the wax only due to heat.
• D. Air becomes flammable over time.

Explanation: The correct answer is B: Oxygen is necessary for combustion and is used up. The observation of the flame extinguishing and condensation appearing inside the closed bell jar indicates that oxygen, essential for combustion, was consumed by the burning candle. Option A is incorrect as carbon dioxide does not support combustion. Option C is incorrect as the condensation is not solely due to the release of water from the wax. Option D is incorrect as air does not become flammable over time.

238. Experiment: Dilute nitric acid was added to powdered iron in a beaker.Observation: A brown gas was released, and the solution turned light green.Question: What does this indicate?

• A. Iron gets coated with brown rust.
• B. Green color is due to iron oxidation into Fe³⁺.
• C. Gas is hydrogen released during rusting.
• D. Iron reacts with nitric acid to form iron nitrate and NO₂.

Explanation: The brown gas observed is nitrogen dioxide (NO₂) formed when iron reacts with nitric acid. The light green solution indicates the formation of iron nitrate. The other options are incorrect because they do not align with the specific observations mentioned in the experiment.

239. Experiment: Carbon dioxide was passed through limewater and then in excess.Observation: Limewater turned milky, then became clear again.Question: What does this show?

• A. Calcium carbonate is a white, insoluble solid that forms when carbon dioxide reacts with limewater, not colored or volatile.
• B. Initially, carbon dioxide reacts with limewater to form insoluble calcium carbonate, which causes the milkiness. When excess CO₂ is added, the calcium carbonate dissolves to form soluble calcium hydrogen carbonate, making the solution clear again.
• C. CO₂ does react with limewater to form calcium carbonate, leading to the initial milkiness observed in the experiment.
• D. The milkiness observed is due to the formation of calcium carbonate, not related to oxygen content. This option misinterprets the observation.

Explanation: When carbon dioxide reacts with limewater (calcium hydroxide), it forms calcium carbonate, which is initially insoluble and causes the milkiness. With excess CO₂, the calcium carbonate then dissolves to form soluble calcium hydrogen carbonate, resulting in a clear solution again. The correct answer explains this chemical reaction sequence accurately. Options A, C, and D provide incorrect interpretations or associations that do not align with the experimental observations.

240. Experiment: Two colorless liquids (ethanol and water) were mixed and the temperature increased.Observation: The beaker felt warm to touch.Question: What kind of process occurred?

• A. Endothermic process due to energy absorption.
• B. Neutralization reaction between acid and base.
• C. Cooling due to evaporation.
• D. Exothermic process due to bond formation.

Explanation: The correct answer is Option D: Exothermic process due to bond formation. The increase in temperature and the warmth observed indicate that heat was released during the process, which is characteristic of an exothermic reaction. In this case, the mixing of ethanol and water led to the formation of new bonds between the molecules, releasing energy in the form of heat. The other options are incorrect because there is no indication of energy absorption, neutralization reaction, or cooling due to evaporation in the experiment and observation provided.