Free Scientific Reasoning MCQs with Answers

31. The figure shows a table where some cutlery is placed on top of a table cloth. When the table cloth is pulled quickly, it is possible that the cutlery lands directly on the same spot on the table and does not get carried away with the cloth. Which of the following serves as a reasonable explanation?

• A. The rapid pulling of the table cloth causes the plates and cloth to become charged with static electricity. This repulsion of like charges creates a levitation force that subtly lifts the cutlery.
• B. The quick pulling action combined with the cutlery's inertia prevents any substantial movement of the cutlery.
• C. The cloth is slippery and offers no friction, allowing it to be easily pulled out from under the cutlery.
• D. The cutlery remains in the same position due to the gravitational force holding it down.

Explanation: The main reason the cutlery remains in place when the table cloth is pulled quickly is due to inertia. Inertia is the tendency of an object to resist changes to its state of motion. When the cloth is pulled swiftly, the cutlery's inertia helps it stay in its original position because the force exerted by the friction between the cloth and the cutlery is minimized due to the high speed of the action. In contrast, if the cloth is pulled slowly, the frictional force would have enough time to act on the cutlery, potentially moving it along with the cloth. Therefore, options C and D are incorrect, as they incorrectly attribute the cutlery's stable position to factors other than inertia.

32. The carpet moves while the dust particles remain stationary due to inertia, causing a separation of dust from the carpet. Why does this happen?

• A. The carpet's motion is resisted by the dust particles' inertia, causing the dust to separate.
• B. The friction from beating charges the carpet, causing it to repel the dust.
• C. The carpet exerts a reaction force on the dust particles, pushing them off.
• D. None of these explanations are correct.

Explanation: The inertia of the dust particles residing on the carpet resists the change in the carpet's motion. Therefore, the carpet's forward motion exerts an apparent backward force (no real force is exerted, this is just apparent due to inertia) on the dust particles, setting them in motion in the opposite direction. This is why the dust comes out of the carpet when beaten.

33. Why do satellites not come falling down to Earth due to gravity?

• A. The gravitational pull of the Sun counteracts Earth's gravity, keeping satellites in orbit
• B. The balance between gravitational pull and centrifugal force keeps satellites in their orbit
• C. They are continually falling towards Earth but move forward fast enough to maintain a stable orbit
• D. They rely on onboard propulsion systems to stay in orbit

Explanation: Satellites remain in orbit due to the interplay between their velocity and Earth's gravitational pull. They are in a state of continuous free fall towards Earth due to gravity. However, their horizontal velocity is so high that they keep missing Earth, resulting in an orbit.Option A incorrectly attributes the Sun's gravitational pull as a balancing factor, which is not the case. Option B mentions centrifugal force, which is a fictitious force when viewed from a rotating frame and not applicable here.Option C correctly identifies that satellites are always falling towards Earth, but their forward velocity keeps them in orbit. Option D mistakenly attributes the use of propulsion systems for maintaining orbit, which is not necessary for stable orbiting due to the satellite's initial velocity.

34. The speed at which neurons conduct nerve impulses depends upon the rate of diffusion of sodium and potassium ions as well as on the resistance of the nerve fibers. Why do myelinated axons of frogs, having a diameter of 3.5µm conduct impulses at speeds of 30ms-1 whereas myelinated axons of the same diameter in a cat, conduct impulses at speeds of 90ms-1?

• A. Cats are warm-blooded whereas frogs are cold-blooded
• B. Concentration gradients of potassium and sodium are steeper in cats
• C. The cats have more neurons transmitting the same signal
• D. Neurons in cats have smaller refractory periods

Explanation: The correct answer is that cats are warm-blooded whereas frogs are cold-blooded. Warm-blooded animals maintain a constant and generally higher body temperature, which accelerates many physiological processes, including nerve impulse conduction. The speed at which nerve impulses are conducted is influenced by the temperature of the organism, with higher temperatures typically enhancing conduction velocity.Option B is incorrect because although ion concentration gradients play a role in nerve impulse conduction, they are not the primary reason for the speed difference between cats and frogs. Option C is incorrect because the number of neurons does not affect the conduction speed of individual neurons. Option D is incorrect because the refractory period affects how quickly a neuron can fire again after an impulse, not the speed of conduction of a single impulse.

35. Why is color blindness more common in males than in females?

• A. Men do not take care of their eyes well enough
• B. Men spend more time in front of digital screens than women
• C. Men usually aren't able to distinguish between colors due to some circuitry in their right hemisphere of the brain
• D. Color blindness is a sex-linked genetic disorder

Explanation: Color blindness is more common in males because it is a sex-linked genetic disorder primarily associated with the X chromosome. Males have only one X chromosome, inherited from their mother. If that X chromosome carries the gene for color blindness, they will express the condition because they do not have a second X chromosome to potentially counteract it. Conversely, females have two X chromosomes, so a non-affected X chromosome can compensate for one that carries the gene for color blindness, reducing the likelihood of expressing the condition.The other options are incorrect because they attribute color blindness to non-genetic factors like eye care, screen time, or brain circuitry, none of which are relevant to the genetic inheritance of color blindness.

36. Which bacteria are responsible for the formation of curd?

• A. Lactic acid bacteria
• B. Lactobacillus acidophilus
• C. Lactobacillus aureus
• D. Bacillus radicicola

Explanation: Curd may contain a wide variety of bacteria like Lactobacillus acidophilus, Lactococcus lactis, Lactococcus lactis cremoris, etc. These bacteria then carry out fermentation of lactose present in the milk to form lactic acid which lowers the pH and causes agglutination of milk proteins and hence curd formation.

37. Why does the Sun appear red at sunset and sunrise?

• A. The Sun's nuclear reactions change intensity at sunset, altering its color to red.
• B. The Sun emits different colors from different areas, and at sunset, we see the red part.
• C. During sunset, the sun's rays travel through more atmosphere, scattering shorter wavelengths and leaving red light to dominate.
• D. Plants emit red pigments at sunset, which color the sky red.

Explanation: The Sun appears red at sunset and sunrise due to the scattering of light in the Earth's atmosphere. As the Sun is close to the horizon, its light has to pass through a larger thickness of the atmosphere. Shorter wavelengths of light (like blue and violet) are scattered out, leaving primarily the longer wavelengths, such as red and orange, to reach the observer's eyes. This is why the Sun appears red. The other options are incorrect because they either misunderstand the nature of the Sun or incorrectly attribute the sky's color to unrelated factors.

38. How much does the sky weigh?

• A. 5.2 million billion metric tons
• B. 12 billion kilograms
• C. 1000 kilograms
• D. The sky does not have weight

Explanation: The correct answer is that the sky, or more accurately the Earth's atmosphere, weighs approximately 5.2 million billion metric tons. This is derived from the average atmospheric pressure of 14.7 pounds per square inch, which equates to about 6.6 kilograms per square inch, over the entire surface area of the Earth. This pressure is exerted by the weight of the air above us. Option A correctly captures this immense weight. Option B and Option C significantly underestimate this weight, failing to account for the vast volume and coverage of the atmosphere. Option D mistakenly suggests the sky has no weight, ignoring the gravitational effect on the atmospheric gases.

39. What would be the total weight of all humans on Earth combined, approximately, if the average weight of a human is 40 kg and the population is 8 billion?

• A. 7 billion kg
• B. 320 billion kg
• C. 320 million kg
• D. 2 billion kg

Explanation: The total weight of all humans on Earth can be calculated by multiplying the average weight of a person, 40 kg, by the global population, 8 billion. This gives us a total of 320 billion kg. Option A, 7 billion kg, suggests an average weight of less than 1 kg, which is far too low. Option C, 320 million kg, implies an average weight of 0.04 kg per person, which is not possible. Option D, 2 billion kg, assumes an average weight of 0.25 kg per person, which is also incorrect.

40. Honey is sweeter than cane sugar or corn syrup. Which one of the following carbon sugars is responsible for this

• A. Dextrose
• B. Lactose
• C. Sucrose
• D. Fructose

Explanation: DFructose is present in honey which is sweeter than sucrose present in corn syrup or cane sugar