Free Scientific Reasoning MCQs with Answers

71. Due to positioning of the fetus, the umbilical cord becomes twisted and fails to function properly. What problem will this causes for the fetus?

• A. Lower birth weight
• B. Brain damage from low oxygen supply
• C. Malnutrition
• D. All of the above

Explanation: The umbilical cord provides oxygen and nutrients to the fetus. A lack of its functionality would lead to all of the above mentioned symptoms

72. The skeleton of a mamoth was recently recovered from a permafrost mine in the United States. Analysis of the elements in the mammoth showed 1/32th of the expected levels of carbon-14 isotope. If the half life of carbon-14 may be considered to be 5730 years, how many years ago did this mammoth exist?

• A. 5,730 years
• B. 11,460 years
• C. 32,300 years
• D. 28,650 years

Explanation: Half-life is the amount of time required for a substance to decrease to half its initial value. Carbon-14 must have undergone 5 half-lives to reach the 1/32 level. Hence, 5 x 5730 years have passed since the mammoth lived. 5 x 5730= 28650

73. Which of the following is NOT sufficient to measure the resistance of an unknown resistor?

• A. Battery, voltmeter, ammeter, connecting wires, switch
• B. Battery, galvanometer, 3 known resistors, switch, connecting wires
• C. Battery, ohmmeter, connecting wires
• D. Battery, ammeter, galvanometer, switch, connecting wires

Explanation: The correct answer is Option D. This setup does not have the necessary equipment to measure voltage or resistance directly, as it lacks both a voltmeter and an ohmmeter. An ammeter alone cannot provide the necessary data to calculate resistance without a corresponding voltage measurement.Options A and C are sufficient because they involve either a direct resistance measurement with an ohmmeter or the application of Ohm's Law using both current and voltage measurements. Option B is also sufficient as it effectively uses a Wheatstone bridge to determine the unknown resistance through balance, a known and reliable method.

74. The figure shows Ahmad, standing on an elevator which is moving front he fourteenth floor to the fourth floor. Ahmad initially stood on a weighing scale to see that his mass was 60kg at rest. If the acceleration of the elevator is 2m/s2, what reading does the scale show? (g=10m/s2)

• A. 60kg
• B. 72kg
• C. 48kg
• D. 80kg

Explanation: When the elevator falls in the direction of gravity, the relative acceleration decreases from 10 to 8m/s2. If at 10m/s2, the reading was 60kg, then at 8m/s2, the reading is 60x8/10= 48kg

75. Why is the ozone layer so important for our survival?

• A. It provides air resistance to objects entering Earth, causing them to burn up.
• B. Ozone breaks down into oxygen which is essential for breathing.
• C. Ozone traps harmful chemicals like chlorine to prevent tissue damage.
• D. The ozone layer absorbs harmful ultraviolet radiation from the sun.

Explanation: The stratospheric ozone layer is crucial because it acts as Earth's "sunscreen," absorbing the majority of the sun's harmful ultraviolet (UV) radiation. This protection is vital as excessive UV radiation can lead to skin cancer, cataracts, and other health issues, as well as harm ecosystems and wildlife. The other options are incorrect because they attribute roles to the ozone layer that belong to the broader atmosphere or misrepresent its chemical interactions.

76. Erythrocytes are the functional component of blood responsible for the transportation of gasses and nutrients throughout the human body. Their unique shape and composition allow for these specialized cells to carry out their essential functions. Erythrocytes would swell and burst if placed in conditions:

• A. Temperature of 310 K
• B. 15% NACL solution
• C. 15% Hydrochloric acid
• D. 0.15% NACL solution

Explanation: This is a hypotonic solution (lower concentration of solutes). Hypotonic solutions can cause cells to take in water and swell. In extreme cases, it could lead to bursting (hemolysis) of erythrocytes.

77. How many chain isomers can an aliphatic saturated hydrocarbon with 7 carbons make?

• A. 7
• B. 5
• C. 12
• D. 9

Explanation: An aliphatic saturated hydrocarbon with 7 carbons is an alkane, represented by the formula C₇H₁₆. Chain isomerism occurs when the carbon skeleton of the molecule can be rearranged in different ways, resulting in different compounds with the same molecular formula. For C₇H₁₆, there are exactly 9 distinct arrangements or chain isomers possible. Hence, the correct answer is 9.Option A (7) is incorrect because it underestimates the number of possible isomers. Option B (5) is also incorrect as it is an underestimation. Option C (12) overestimates the number of isomers. Therefore, Option D (9) is the only correct choice.

78. Based on table 1, of the following 4 metals, which has the greatest ability to carry electric current?

• A. Beryllium
• B. Iron
• C. Magnesium
• D. Tungsten

Explanation: As shown in the table, out of all four metals listed, beryllium has the highest conductivity value i.e 2.81

79. A pyrethroid is an organic compound similar to the natural pyrethrins, which are produced by the flowers of pyrethrums.Pyrethroids are used as commercial and household insecticides.Pyrethroid is an organic compound produced by the flowers of pyrethrums. Scientists found that even in a bee populated area, the bees were not found near the pyrethrums. After further research they concluded that pyrethroid is a defensive chemical produced by these plants to keep bees away from the flowers by affecting the neurochemical pathway of the bees. Scientists further researched and developed a synthetic pyrethroid and was introduced as an insecticide on a commercial scale to farmers in the early 1900s. Initially it was very successful in keeping insects away. However, after a while the farmers started feeling severe mood swings and nausea on a daily basis. Later, scientists further studied the insecticide and deduced that the insecticide in large quantities also affected the neurochemical pathways of the farmers and reduced the synthesis of a neurotransmitter in the brain. Which neurotransmitter did the Pyrethroid affect in the farmers who used the insecticide in a large quantity

• A. Acetylcholine
• B. Serotonin
• C. Calcitonin
• D. GABA

Explanation: The information provided suggests that the synthetic pyrethroid affected the neurochemical pathways of the farmers and reduced the synthesis of a neurotransmitter in the brain. In this context, the correct answer is serotonin.Serotonin is a neurotransmitter that plays a crucial role in regulating mood, emotion, and appetite. Imbalances in serotonin levels have been associated with mood disorders, and the reduction in serotonin synthesis could contribute to symptoms like severe mood swings and nausea, as mentioned in the scenario.It's important to note that neurotransmitters such as acetylcholine, calcitonin, and GABA are not typically associated with the regulation of mood and emotions in the same way as serotonin. Therefore, in the given context, serotonin is the neurotransmitter that the pyrethroid affected in the farmers who used the insecticide in large quantities.

80. Ethanol and Propane are both colorless organic substances of a similar molar mass with 2 and 3 carbon atoms respectively. However, despite having a longer carbon chain, propane is a gas and ethanol, having less carbon atoms is a liquid at room temperature. What is the reason behind the differences observed

• A. Ionic bonding in ethanol
• B. Greater dispersion forces in ethanol
• C. Dipole forces between the O and H in the ethanol molecule
• D. Hydrogen bonding between molecules of ethanol

Explanation: The key factor explaining the difference in physical state between ethanol and propane is the presence of hydrogen bonding in ethanol. While propane primarily experiences dispersion forces due to its larger size, ethanol molecules can form hydrogen bonds.Hydrogen bonding is a stronger intermolecular force than dispersion forces, and it contributes to the higher boiling point of ethanol. As a result, ethanol is a liquid at room temperature, while propane, which lacks hydrogen bonding, is a gas.