UPSC 1997 Science and Technology Questions with Answers

Explanation

Options (a), (b) and (c) are incorrect: Protein analysis lacks the precision needed for identifying individual genetic relationships, as protein expression can be influenced by multiple factors. Chromosome counting determines the number of chromosomes but cannot identify specific genetic relationships. Quantitative analysis of DNA measures the quantity of DNA but does not provide the unique genetic markers necessary for establishing paternity.

Option (d) is correct: DNA fingerprinting is the most accurate and reliable technique to establish paternity. This method analyzes specific regions of the DNA that are highly variable among individuals, called short tandem repeats (STRs). A child inherits half of their DNA from the mother and the other half from the father, making DNA fingerprinting a powerful tool to match the genetic profiles of the child and the alleged parent.

Explanation

Surface tension is the force that acts on the surface of a liquid, causing it to contract and minimize its surface area. This effect occurs because molecules at the surface of the liquid experience a net inward force due to the attractive forces between the molecules. As a result, the liquid tends to form shapes that have the least surface area, such as spherical droplets. This tendency to minimize surface area is why liquid droplets form spherical shapes in free space, as a sphere has the smallest surface area for a given volume.

Explanation

A vector quantity is a physical quantity that has both magnitude and direction. In addition to how much of a quantity there is, you also need to know the direction in which it acts. Some examples of vector quantities include force, velocity, acceleration and displacement. Momentum is a vector quantity because it has both magnitude and direction (it depends on the direction of motion and the velocity of the object).

Explanation

Option (a) is correct: The working principle of a washing machine is Centrifugation. It is a process used to separate substances of different densities by spinning them at high speed. In a washing machine, the centrifugal force generated during the spin cycle helps remove water from the clothes along with dirt and stain.

Option (b), (c) and (d) are incorrect:

Dialysis is a process used to remove waste products and excess fluids from the blood in patients with kidney failure. It involves the diffusion of solutes across a semipermeable membrane. Reverse osmosis is a water purification process that uses a semipermeable membrane to remove ions, molecules and larger particles from water. It is commonly used in desalination and water filtration systems. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. While diffusion plays a role in processes like the mixing of detergents in water but it is not the main working principle of a washing machine.

Explanation

Paramagnetism refers to the property of a material that is weakly attracted to an external magnetic field due to the presence of unpaired electrons in its atomic or molecular structure. When placed in a magnetic field, these unpaired electrons align their magnetic moments in the direction of the field, causing a weak but positive magnetization. However, this effect disappears once the external field is removed.

Option (c) is correct: Oxygen (O₂) is paramagnetic because it has two unpaired electrons in its molecular orbital configuration, making it weakly attracted to a magnetic field. Options (a), (b) and (d) are incorrect:

Iron is ferromagnetic (not always paramagnetic), meaning it is strongly attracted to magnetic fields. Hydrogen and Nitrogen are diamagnetic, meaning they are weakly repelled by magnetic fields due to their paired electrons. Directions: The following item consists of two statements, one labeled as the Assertion (A) and the other as Reason (R). You have to answer this item using the code given below.

Explanation

A comet is a small celestial body composed of ice, dust, and rocky material that orbits the Sun in an elliptical path. When it gets close to the Sun, the heat causes its icy nucleus to vaporize, forming a glowing coma.

Option (c) is correct: The tail of a comet is directed away from the Sun due to the solar wind and radiation pressure exerted by the Sun. The Sun emits charged particles (mainly electrons and protons) that interact with the comet’s nucleus and coma, pushing gas and dust away. This creates a glowing tail that always points opposite the Sun, regardless of the comet’s orientation. The tail’s direction can change as the comet moves, influenced by factors like solar wind intensity, the coma’s shape, and the Sun’s magnetic field.

Explanation

Fluorine is the most reactive halogen because:

Small Atomic Size: Fluorine has the smallest atomic radius among halogens, leading to a strong attraction for electrons. High Electronegativity: It is the most electronegative element in the periodic table, making it highly effective in gaining electrons. Low Bond Dissociation Energy: The F-F bond in molecular fluorine is weak due to electron repulsion between the two small atoms, which makes it highly reactive. Reactivity Trend in Halogens:

Fluorine > Chlorine > Bromine > Iodine

Explanation

The distinctive pungent odour of garlic is due to sulphur-containing compounds, mainly allicin. These compounds are formed when alliin is converted by the enzyme alliinase during chopping or crushing.

Explanation

Eugenol is the active component in clove oil, contributing to its distinct aroma and analgesic properties. It is widely used in dental care and as a natural preservative.

Explanation

Mustard gas (sulfur mustard) was widely used as a chemical weapon during World War I. It causes blistering of the skin and mucous membranes, along with severe respiratory damage.