Explanation: Cadmium (Cd) is a toxic heavy metal released from industrial waste, batteries, and mining processes. When it enters the food chain (especially through contaminated rice or water), it accumulates in the body and affects the kidneys, causing protein loss in urine and kidney failure. It is also associated with Itai-Itai disease in Japan, characterized by kidney damage and brittle bones.

Explanation: Lysergic acid diethylamide (LSD) was discovered by Dr. Albert Hofmann, a Swiss chemist, in 1938 at the Sandoz Laboratories in Switzerland. LSD is a powerful hallucinogenic compound derived from lysergic acid, which occurs in the fungus Claviceps purpurea (ergot) that grows on rye. Hofmann accidentally discovered its psychological effects in 1943 when he absorbed a small amount through his skin, leading to vivid visual hallucinations. LSD acts on serotonin receptors in the brain and profoundly alters perception and mood.

Explanation: Measles is a highly contagious disease caused by the Measles virus, which belongs to the Paramyxoviridae family, genus Morbillivirus. It spreads through respiratory droplets from coughing or sneezing by an infected person. Common symptoms include high fever, cough, runny nose, red eyes, and a characteristic red skin rash. Severe cases can lead to pneumonia or encephalitis. Measles can be effectively prevented by the MMR vaccine (Measles, Mumps, and Rubella).

The pale yellow colour of urine is due to the presence of the pigment Urochrome. Urochrome is a waste product formed from the breakdown of hemoglobin in red blood cells. It is produced when hemoglobin is metabolized into urobilin and then excreted through urine. The intensity of the yellow color can vary depending on hydration levels — darker urine indicates dehydration, while pale urine indicates proper hydration.

Other options (for context)

• Urophyll: No such pigment exists in human physiology.
• Chlorophyll: Green pigment found in plants, not in urine.
• Chloroplast: Cell organelle in plants where photosynthesis occurs, not a pigment.

Explanation: The speed of internet connectivity is expressed in Megabits per second (Mb/sec or Mbps). It indicates how much data is transferred per second over a network connection. One megabit equals 1,000,000 bits. Higher Mbps values mean faster internet speeds. For example, a 100 Mbps connection can transfer 100 million bits of data every second. Note that 1 byte = 8 bits, so internet speeds in Mbps differ from file sizes, which are usually measured in megabytes (MB).

Explanation: The burning of a candle is a chemical change because new substances such as carbon dioxide, water vapour, and heat energy are produced during the reaction between wax and oxygen. This change is irreversible and results in a permanent alteration of the chemical composition of the material. In contrast, melting of wax and vapourisation of water are physical changes since no new substances are formed and the process can be reversed by cooling.

Explanation: The rusting of iron is an example of oxidation. When iron reacts with oxygen and moisture from the air, it forms hydrated ferric oxide (Fe₂O₃·xH₂O), commonly known as rust. This process involves the loss of electrons by iron, which is a characteristic feature of oxidation.

Explanation: EDUSAT (Education Satellite) was launched by the Indian Space Research Organisation (ISRO) in September 2004. It was the first Indian satellite built exclusively for educational purposes, designed to provide distance learning and interactive education through satellite communication.

Explanation: Vitamins are classified into two categories based on their solubility — fat-soluble and water-soluble. Vitamin C (ascorbic acid) and the B-complex vitamins are water-soluble, meaning they dissolve in water and are not stored in the body. Therefore, they must be consumed regularly through diet. Deficiency of Vitamin C causes scurvy, characterized by bleeding gums and delayed wound healing.

Explanation: The intensity of sound is measured in decibels (dB). The decibel is a logarithmic unit that expresses the ratio of a sound’s intensity compared to a reference level (usually the faintest sound the human ear can detect, known as the threshold of hearing). The higher the decibel value, the louder the sound. For example, normal conversation is around 60 dB, traffic noise is about 80–90 dB, and sounds above 120 dB can cause pain or hearing damage.