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Free Scientific Reasoning MCQs with Answers

334 Scientific Reasoning MCQs from Analytical and Logical Reasoning, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Scientific reasoning evaluates hypotheses through observations, variables, controls, measurements and experimental results. Questions involve identifying independent and dependent variables, recognising a fair test, interpreting tables or graphs, distinguishing evidence from opinion, and deciding whether data supports, rejects or leaves a hypothesis unresolved.

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334 questions · page 12 of 17

221. Experiment: Two groups of mice were fed diets with and without iodine for four weeks. Thyroid size and hormone levels were then measured.Observation: Mice on iodine-deficient diets had enlarged thyroids and low hormone levels.Question: What is the most valid conclusion?

  • A. Thyroid size decreases with iodine deficiency.
  • B. Iodine causes thyroid suppression.
  • C. Iodine is essential for normal thyroid hormone production.
  • D. Diet has no impact on endocrine glands.

Explanation: The correct conclusion is that iodine is essential for normal thyroid hormone production.

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Correct answer: Iodine is essential for normal thyroid hormone production.

222. Experiment: To test photoperiodism, plants were exposed to 8, 12, and 16 hours of light daily. Flowering time was recorded.Observation: Plants under 12 hours light flowered earlier than others.Question: What does this indicate?

  • A. Plants respond to light duration to regulate flowering.
  • B. More light always delays flowering.
  • C. Light has no effect on plant reproduction.
  • D. Darkness is harmful to flower development.

Explanation: The correct answer is that plants respond to light duration to regulate flowering.

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Correct answer: Plants respond to light duration to regulate flowering.

223. Experiment: A water plant was placed in water with baking soda under sunlight. Bubble count was recorded over 30 minutes.Observation: More bubbles were released compared to water without baking soda.Question: What does this show?

  • A. Increased CO₂ from baking soda enhances photosynthesis.
  • B. Baking soda reduces light absorption.
  • C. Bubbles are due to root respiration.
  • D. CO₂ suppresses oxygen production.

Explanation: The experiment demonstrates that baking soda, by releasing CO₂ in water, boosts photosynthesis in the water plant.

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Correct answer: Increased CO₂ from baking soda enhances photosynthesis.

224. Experiment: Fruit juice was treated with different enzymes (pectinase, cellulase, amylase). Juice clarity was observed.Observation: Pectinase-treated juice was clearer than others.Question: What is the likely reason?

  • A. Amylase is responsible for breaking down starch into sugars.
  • B. Cellulase breaks down cellulose into glucose.
  • C. Enzymes have specific functions beyond just reducing pH.
  • D. Pectinase breaks down pectin, improving juice clarity.

Explanation: The correct answer is option D. Pectinase breaks down pectin, a substance that can cause cloudiness in fruit juice.

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Correct answer: Pectinase breaks down pectin, improving juice clarity.

225. Jimmy is training for a long-distance cycling race. At the end of each week, he records the tota training until the end of that results are shown on the following graph.Which one of the following could represent the distance that Jimmy has cycled the week?

  • A. A
  • B. B
  • C. C
  • D. D

Explanation: The correct answer is option D because it aligns with the data points on the graph, indicating the distance that Jimmy has cycled during…

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Correct answer: D

226. Experiment: Two groups of rats were raised in different light conditions-one in constant light, the other in a normal light-dark cycle. Melatonin levels were measured.Observation: Rats in constant light had lower melatonin levels than those in a light-dark cycle.Question: What conclusion is supported?

  • A. Rats produce melatonin regardless of lighting.
  • B. Melatonin production is influenced by light exposure.
  • C. Constant light increases melatonin.
  • D. Melatonin is not related to light cycles.

Explanation: The correct answer is Option B: Melatonin production is influenced by light exposure.

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Correct answer: Melatonin production is influenced by light exposure.

227. The other day I saw an alien spacecraft, which had some strange markings on the underside, hovering overhead. My three friends and I each made a drawing of these markings as the craft rotated slowly above us.Three of us drew them correctly. Which of the following drawings is wrong?

  • A. A
  • B. B
  • C. C
  • D. D

Explanation: The correct answer is Option A, as it aligns with the description of the markings seen on the alien spacecraft.

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Correct answer: A

228. Experiment: To test geotropism, potted plants were placed horizontally and left for 3 days. Root and shoot directions were noted.Observation: Roots grew downward while shoots curved upward.Question: What is the most appropriate conclusion?

  • A. Roots grow randomly regardless of gravity.
  • B. Roots and shoots respond to gravity in opposite directions.
  • C. Geotropism only affects aquatic plants.
  • D. Shoots follow gravity just like roots.

Explanation: In this experiment, the observation that roots grew downward while shoots curved upward indicates that roots and shoots respond to gravity…

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Correct answer: Roots and shoots respond to gravity in opposite directions.

229. Experiment: A fungal culture was grown at 10°C, 25°C, and 40°C. Growth diameter was measured every day.Observation: Maximum growth occurred at 25°C; very little at 10°C and 40°C.Question: What can be concluded?

  • A. Fungi grow best at very high temperatures.
  • B. Cold promotes fungal reproduction.
  • C. There is an optimal temperature for fungal growth.
  • D. Temperature has no impact on fungi.

Explanation: The correct answer is 'There is an optimal temperature for fungal growth' because the experiment showed that maximum growth occurred at…

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Correct answer: There is an optimal temperature for fungal growth.

230. Experiment: Two glasses were filled with water. One had detergent added and both were used to water plants over 5 days.Observation: Plants watered with detergent showed wilting and reduced growth.Question: What is the likely explanation?

  • A. Plants use detergents for photosynthesis.
  • B. Detergents stimulate plant growth hormones.
  • C. Detergents disrupt cell membranes and root absorption.
  • D. No effect is expected from detergent in water.

Explanation: The correct answer is Option C: Detergents disrupt cell membranes and root absorption.

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Correct answer: Detergents disrupt cell membranes and root absorption.

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.

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Correct answer: $34

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…

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Correct answer: Copper ions are transferred but concentration stays constant.

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…

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Correct answer: Reaction rate decreases as reactants are used up.

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.

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Correct answer: A compound (iron sulfide) was formed with unique properties.

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.

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Correct answer: Latent heat of fusion keeps temperature constant during phase change.

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.

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Correct answer: Hydrogen, due to reaction of metal with 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.

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Correct answer: Oxygen is necessary for combustion and is used up.

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

Explanation: The brown gas observed is nitrogen dioxide (NO₂) formed when iron reacts with nitric acid.

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Correct answer: Iron reacts with nitric acid to form iron nitrate and NO₂.

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. The milkiness observed is due to the formation of calcium carbonate, not related to oxygen content. This option misinterprets the observation.
  • C. CO₂ does react with limewater to form calcium carbonate, leading to the initial milkiness observed in the experiment.
  • D. 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.

Explanation: When carbon dioxide reacts with limewater (calcium hydroxide), it forms calcium carbonate, which is initially insoluble and causes the…

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Correct answer: 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.

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.

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Correct answer: Exothermic process due to bond formation.
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