Explanation: To read small letters, a convex lens (converging lens) with a short focal length such as 5 cm is used as a magnifying glass. It produces an enlarged, upright, and virtual image of the object, making tiny text appear bigger and clearer to the eye.

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: Normal human blood has a slightly alkaline pH of 7.35 to 7.45. This pH is maintained by buffer systems such as the bicarbonate buffer system and controlled by the lungs (CO₂ regulation) and kidneys (acid-base balance). A deviation from this range can be life-threatening — acidosis occurs if pH falls below 7.35, and alkalosis occurs if it rises above 7.45.

Explanation: Acids do not turn red litmus to blue; they turn blue litmus paper red. Acids are sour in taste, corrosive in nature, and have a pH value less than 7. The statement that acids turn red litmus to blue is incorrect.

Neil Armstrong was the first man to land on the Moon on July 20, 1969, during NASA’s Apollo 11 mission. He became the first human to step onto the lunar surface, famously saying, "That's one small step for man, one giant leap for mankind." His historic achievement marked a major milestone in space exploration.

Other options (for context)

• Aldrin: Refers to Buzz Aldrin, the second man to walk on the Moon, who accompanied Armstrong on Apollo 11.
• Michael Collins: The third member of the Apollo 11 crew, who orbited the Moon in the command module but did not land.
• Gagarin: Refers to Yuri Gagarin, the first human to travel into space in 1961, but he never landed on the Moon.

Explanation: Although most non-metals do not conduct electricity, graphite is an exception. In graphite, each carbon atom is bonded to three others, leaving one free electron that moves freely between layers, allowing it to conduct electricity efficiently.