Explanation: Sound travels fastest in steel because it is a solid material where the particles are packed very closely together. Sound waves need a medium to travel, and their speed depends on how quickly vibrations can pass from one particle to another. In solids, particles are tightly bound, so vibrations are transmitted more efficiently. In contrast, sound travels slower in liquids and slowest in gases. It cannot travel through a vacuum because there are no particles to carry the vibrations.

In medical terminology, USG stands for Ultrasonography. It is a diagnostic imaging technique that uses high-frequency sound waves to create images of internal organs, tissues, and developing fetuses. USG is commonly used in obstetrics, cardiology, and abdominal examinations as it is safe and non-invasive.

• Undersized gland: Not a recognized medical term.
• Unsegmented gonads: Incorrect and unrelated to imaging.
• None of the above: Incorrect as option B is correct.

Nitrous oxide (N₂O) is an anaesthetic gas, commonly known as laughing gas. It is used in dentistry and minor surgeries to induce mild anesthesia and relaxation. It acts quickly and wears off rapidly, making it safe for short medical procedures.

• Nitrogen dioxide: A toxic air pollutant, not used as anesthesia.
• Nitric oxide: A signaling molecule in the body, not an anesthetic.
• Nitrogen: An inert gas, does not induce anesthesia.

Explanation: PARAM 8000 is India's first supercomputer, developed in 1991 by the Centre for Development of Advanced Computing (C-DAC) under the leadership of Dr. Vijay Bhatkar. It marked India’s entry into high-performance computing and was capable of 1 GigaFLOP (one billion calculations per second).

Explanation: The Sinoatrial (SA) node is a specialized group of modified cardiac muscle fibers located in the right atrium of the heart, near the opening of the superior vena cava. It generates electrical impulses (action potentials) that initiate each heartbeat. Therefore, it is known as the natural pacemaker of the heart.

The impulses from the SA node spread across the atria, causing them to contract, and are then transmitted to the Atrioventricular (AV) node, Bundle of His, and Purkinje fibers to coordinate ventricular contraction.

Normal rate of SA node firing: ~70–75 impulses per minute (in a healthy adult at rest).

In case of SA node failure: Artificial pacemakers are implanted to maintain normal rhythm.

Green leafy vegetables are a rich source of Folic Acid (Vitamin B₉). Folic acid is essential for the formation of red blood cells, DNA synthesis, and proper cell growth. It is particularly important for pregnant women, as it helps prevent neural tube defects in the developing fetus. Vegetables like spinach, kale, lettuce, and fenugreek leaves are excellent sources of folic acid.

Other options (for context)

• Citric acid: Found mainly in citrus fruits like oranges and lemons.
• Malic acid: Commonly present in apples and other fruits, not in leafy greens.
• None of these: Incorrect — folic acid is the correct nutrient associated with green leafy vegetables.

Explanation: Sound waves with frequencies below 20 Hz are called infrasonic waves. These waves are inaudible to the human ear but can be produced by natural phenomena such as earthquakes, volcanic eruptions, and ocean waves.

Explanation: The main function of the kidneys is to purify blood by removing waste products, excess salts, and extra water from the body in the form of urine. Each kidney contains about one million nephrons, which are the structural and functional units responsible for blood filtration. The kidneys also help in maintaining the acid-base balance, water balance, and blood pressure, and play a role in hormone secretion such as erythropoietin (for RBC production).

Explanation: Vitamin K is produced by gut bacteria (Escherichia coli) in the large intestine. It plays a vital role in the synthesis of prothrombin, a protein essential for normal blood clotting. Although some of it is obtained from food (like leafy vegetables), intestinal bacteria supply a significant portion of the body’s requirement.