Explanation: The hard structure of bones and teeth is primarily made of calcium phosphate in the crystalline form of tricalcium phosphate (Ca₃(PO₄)₂). It provides rigidity and strength. In tooth enamel, a small portion is converted into fluorapatite, which makes teeth resistant to bacterial decay.

Explanation: Marijuana is a psychoactive drug obtained from the female inflorescence (flowering tops) of the Cannabis sativa plant. It contains the active compound tetrahydrocannabinol (THC), which affects the central nervous system and alters mood and perception.

Explanation: Execution time is the period during which a job or program is actively processed by the computer’s CPU. It refers to the actual time taken to execute instructions, excluding waiting or idle times such as input/output delays or queue time.

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.

Other options (for context)

• 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.

Explanation: Dengue fever is caused by the Dengue virus, which belongs to the Flavivirus group. It is transmitted to humans through the bite of an infected Aedes aegypti mosquito. The virus multiplies in the blood and causes symptoms such as high fever, severe headache, joint and muscle pain, rashes, and low platelet count. In severe cases, it can lead to Dengue hemorrhagic fever or Dengue shock syndrome. Prevention includes controlling mosquito breeding and avoiding mosquito bites.

Explanation: Carbon monoxide (CO) is a colorless, odorless, and highly poisonous gas. When inhaled, it competes with oxygen for binding sites on the haemoglobin molecule in red blood cells. CO has approximately 200–250 times greater affinity for haemoglobin than oxygen. As a result, it forms a stable compound called carboxyhaemoglobin (HbCO).

This compound prevents haemoglobin from carrying oxygen to body tissues, leading to oxygen deprivation (hypoxia). Prolonged exposure to CO can cause headache, dizziness, nausea, unconsciousness, and even death due to suffocation.

Chemical Reaction:

Hb + CO → HbCO (Carboxyhaemoglobin)

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: Tuberculosis (TB) is not a viral disease; it is caused by a bacterium called Mycobacterium tuberculosis. In contrast, Polio, Swine flu, and Hepatitis are viral diseases caused by different types of viruses.