Free Scientific Reasoning MCQs with Answers

121. Echinoderms are defined as various invertebrate marine animals characterized by a hard, spiny covering or skin. They have attracted much attention due to their extensive fossil record, ecological importance, and unusual body forms. Although most echinoderms are extinct, many living representatives still exist. All living echinoderms have an internal skeleton and a central body cavity, but their outward appearance can vary significantly. For example, starfish and brittle stars have arms that extend from a central disk; sea lilies have a central stalk, or stem, and resemble flowers; and sea cucumbers are wormlike and tend to burrow. The ways in which echinoderms move and feed are as diverse as their body forms. Table 1 lists certain echinoderms and their methods of locomotion (movement) and feeding. Table 2 includes examples of echinoderm habitats around the world. According to Table 1 and Table 2, crinoids can be found feeding on plankton.

• A. near the shore
• B. in deep ocean trenches
• C. in offshore mud and ooze
• D. on the deep-sea floor

Explanation: The correct answer is C. According to Table 1, sea lilies are classified as crinoids. Table 2 specifies that sea lilies are typically found in offshore mud and ooze, thereby supporting answer choice C. The other options are incorrect because the habitats mentioned do not align with the details provided in Table 2 regarding crinoid habitats.

122. Suppose scientists discover a new echinoderm that uses its tube feet to move across the deep-sea floor as it hunts for prey. This newly discovered echinoderm can most likely be classified as a(n):

• A. Crinoid.
• B. Asteroid.
• C. Ophiuroid.
• D. Holothurian.

Explanation: The correct answer is 'Asteroid.' Asteroids, known as starfish, are predatory echinoderms using their tube feet for motion and are located on the deep-sea floor. The scenario described aligns with these characteristics. Crinoids are primarily suspension feeders and not hunters. Ophiuroids use their arms rather than tube feet for movement and are scavengers. Holothurians usually feed on detritus and are not predators, which rules them out as well.

123. The instrument shown is used to study:

• A. Cell organelles
• B. The flight pattern of birds
• C. Movement of stars in galaxies
• D. Old manuscripts
• E. Human vision defects

Explanation: Binoculars are optical instruments designed for observing distant objects by magnifying them, making them ideal for birdwatching and studying the flight patterns of birds. This distinguishes them from microscopes, which are used for viewing microscopic objects like cell organelles, and telescopes, which are used for astronomical observations. Devices for reading old manuscripts or correcting human vision have different specialized functions and do not relate to the study of birds.

124. When the thermometer was in the 40°C water, in the time interval between 0 sec and 2 sec, approximately how rapidly, in °C/sec, was the temperature registered by the thermometer changing?

• A. 1°C/sec.
• B. 5°C/sec.
• C. 10°C/sec.
• D. 40°C/sec.

Explanation: To answer this question, look at Figure 1. Between 0 and 2 seconds, the thermometer in the 40° water registered a temperature increase from 20° to 30°. Therefore, during the 2-second interval the temperature increased 10°, and the increase in temperature per second was 5°.

125. The three basic crystal structures are called Hexagonal Close Packed (HCP), Face Centered Cubic (FCC) and Body Centered Cubic (BCC).Shown below are alternative representations of the structures in Figure 1.The order in which they are represented is:

• A. BCC, HCP, FCC
• B. BCC, FCC, HCP
• C. FCC, HCP, BCC
• D. HCP, BCC, FCC

Explanation: The correct sequence is Option A: BCC, HCP, FCC. The BCC structure is characterized by atoms at each corner and one in the center of the cube. The HCP structure features a hexagonal arrangement, typically with two layers of closely packed spheres. The FCC structure has atoms located at each face center and corner of the cube. Options B, C, and D misalign these visual identifiers with their respective structures, leading to incorrect sequences.

126. A pantograph is a four-bar linkage mechanism used for drawing. It consists of two long bars and two short bars pivoted to one another so that they can move freely in the plane. In the version shown in Figure 3 below the short bars are half the lengths of the long ones.The point O is held fixed. There is a pointer at X and a pencil at Y. As the pointer at X is traced over a shape, the pencil at Y draws the shape enlarged by a factor of two.In Figure 3 if O and Q are both held fixed, the point Y.

• A. cannot move
• B. can move on a circular path
• C. can move in a straight line
• D. can move freely

Explanation: The pantograph's structure as a four-bar linkage means that when points O and Q are fixed, the movement of point Y is constrained. The linkage creates a situation where Y can only move along a straight path, defined by the geometric configuration and constraints of the linkage. Option A is incorrect because Y can still move, albeit in a restricted manner. Option B is incorrect because the movement is not circular. Option D is incorrect because the movement is not unrestricted; it is specifically linear due to the fixed points.

127. An ideal gas is a hypothetical gas whose pressure - volume - temperature behavior can be completely accounted for by the ideal gas equation (General gas equation). The molecules of an ideal gas do not attract or repel one another, and their volume is negligible compared with the volume of the container. Experiments show that under the STP conditions, one mole of an ideal gas occupies a volume of 22.4dm3.A tin can is sealed at a pressure of 100mmHg. If the can is taken to STP, the can may:

• A. Explode
• B. Collapse
• C. Get larger
• D. Get chilled

Explanation: When the tin can is moved to standard temperature and pressure (STP), the external atmospheric pressure becomes 760 mmHg. Initially, the internal pressure is only 100 mmHg. This significant pressure difference means that the external pressure is much higher than the internal pressure, causing the can to collapse as it tries to equalize the pressure. Option B is correct because collapsing is a result of a higher external pressure compared to the internal pressure. Option A is incorrect because the can cannot explode with a lower internal pressure. Option C is incorrect because getting larger would require a higher internal pressure than external, which is not the case. Option D is incorrect as the transition to STP does not imply significant cooling that would affect the can.

128. It is generally well known that on average we are taller than our ancestor; this is true of people in various places around the world.The people of the Netherlands, now the world's tallest, have been on an upward trend since 1851, though the rate of growth accelerated after the second world war. In 1965, the average Dutchman was 1.78m tall. By 1997, he was 6cm taller. The average Dutch woman grew from 1.66m to 1.71m.The Spanish grew 2.4cm per decade between 1960 and 1990. In Western Europe this growth has now slowed to about 1cm per decade but Western Europe and Japan are increasing by up to 3cm per decade. However, on average, women are increasing in height more slowly than men so the gap in height between the sexes is widening.It has been found that it is the first two years of life which are the most important for height, when the leg bones are growing rapidly. Not only increased food supply but also general health improvement brought about antibiotics and vaccinations have had an effect. Your final height, however, is still dependent on the height of your parents and grandparents.Between 1960 and 1990 the average height of a Spaniard increased overall by about

• A. 3cm
• B. 5cm
• C. 7.2cm
• D. 10cm

Explanation: The text mentions that the Spanish grew by 2.4cm per decade from 1960 to 1990. To find the total growth over these 30 years, multiply the growth per decade (2.4cm) by the number of decades (3). This results in a total increase of 7.2cm

129. Given below is part of a circuit diagram.If the resisters R1 = 5 ohms, R2 = 2 ohms, R3 = 4 ohms, R4 = 12 ohms, R5 = 5 ohms and the current passing through the circuit is 10 amperes. What is the potential difference across b and c?

• A. 112V
• B. 62V
• C. 58V
• D. 280V

Explanation: Given:Step 1: Simplify the parallel part (R₂, R₃, R₄)These 3 resistors are in parallel between b and the left of R₅:Use formula for parallel combination:1/R_parallel = 1/R₂ + 1/R₃ + 1/R₄= 1/2 + 1/4 + 1/12Let's calculate:So,R_parallel = 6/5 = 1.2 ΩStep 2: Add R₅ in seriesR₅ = 5 ΩSo total resistance from b to c:R_bc = R_parallel + R₅ = 1.2 + 5 = 6.2 ΩStep 3: Use Ohm's Law to find potential differenceV = I × R = 10 A × 6.2 Ω = 62 volts

130. If gear (2) moves clockwise, then which of the following directions will be similar to the direction of gear (4)?

• A. Direction of (2) and (5)
• B. Direction of (1) and (2)
• C. Direction of (1), (3) and (5)
• D. Direction of (1), (2) and (5)

Explanation: When gear (2) moves clockwise, gear (3) will move counterclockwise, and gear (4) will move clockwise again, matching the direction of gear (2). Finally, gear (5) will also rotate clockwise if it is connected to gear (4). Thus, gear (4) rotates in the same direction as gears (2) and (5). The other options are incorrect because they involve gears that rotate in the opposite direction or include gears that are not in sync with gear (4).