Explanation: Boron is a vital micronutrient that assists in the uptake and utilization of calcium and maintains the integrity of cell walls and membranes. It also regulates water movement in plant tissues and plays a role in pollen germination and fruit development. Deficiency of boron can lead to poor calcium translocation, brittle tissues, and reduced water absorption.

Aluminium (Al) is the most abundant metal in the Earth's crust, making up about 8.2% by weight. It occurs mainly in the form of bauxite ore (Al₂O₃·2H₂O). Despite being highly abundant, aluminium is never found in its pure form naturally due to its strong reactivity with oxygen. It is widely used in industries for making utensils, aircraft parts, electrical wires, and packaging materials.

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• Zinc: Found in smaller quantities; used in galvanization and alloys.
• Copper: Less abundant; mainly used in electrical wiring.
• Iron: Very abundant but ranks below aluminium in crustal abundance.

William Harvey, an English physician, discovered the process of blood circulation in 1628. He demonstrated that the heart acts as a pump to circulate blood continuously throughout the body via a closed system of arteries and veins. His work, published in "De Motu Cordis" (On the Motion of the Heart and Blood), laid the foundation for modern cardiovascular physiology.

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• Mary Anderson: Invented the windshield wiper, not related to medicine.
• Virginia Apgar: Developed the Apgar score for assessing newborn health.
• Robert Feulgen: Discovered a staining technique for DNA, not blood circulation.

The aorta is the largest artery in the human body. It originates from the left ventricle of the heart and distributes oxygenated blood to all parts of the body through its various branches. The aorta has thick, elastic walls that can withstand the high pressure of blood pumped directly from the heart. It is divided into parts such as the ascending aorta, aortic arch, and descending aorta.

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• Capillary: The smallest blood vessels where exchange of gases and nutrients occurs.
• Vena cava: The largest vein, not an artery; it carries deoxygenated blood back to the heart.
• Pulmonary vein: Carries oxygenated blood from the lungs to the heart but is not the largest vessel.

The purity of milk is tested using a Lactometer. It works on the principle of Archimedes’ principle and is used to measure the specific gravity (density) of milk. Pure milk has a specific gravity ranging between 1.026 and 1.032. If water or other substances are added, the density decreases, indicating adulteration. The lactometer thus helps determine whether the milk is pure or diluted.

Other options (for context)

• Electrometer: Measures electric potential or charge, not related to milk testing.
• Radiometer: Measures radiant energy or light intensity.
• Refractometer: Used to measure refractive index, commonly for sugar solutions, not milk purity.

Explanation: Measles is a highly contagious viral disease caused by the measles virus (a member of the Paramyxovirus group). It spreads through droplets released when an infected person coughs or sneezes. Symptoms include fever, cough, rash, and watery eyes. Other diseases listed — scurvy, asthma, and diabetes — are non-communicable as they do not spread from person to person.

Explanation: The liver is the largest gland in the human body. It is located in the upper right part of the abdomen, just below the diaphragm. The liver performs multiple vital functions, including the secretion of bile (which helps in digestion of fats), detoxification of harmful substances, storage of glycogen (energy reserve), and the synthesis of proteins and cholesterol. It also plays a crucial role in regulating blood sugar levels and metabolism. The average adult human liver weighs about 1.2 to 1.5 kilograms.