The question asks us to evaluate two statements regarding giant stars and dwarf stars, specifically concerning their lifespan and nuclear reaction rates. We need to determine the correctness of each statement individually and then assess if Statement-II explains Statement-I.
A star's lifespan is inversely proportional to its mass and luminosity. Giant stars are typically much more massive and significantly more luminous than dwarf stars. They burn through their nuclear fuel (hydrogen) at a much faster rate due to their higher core temperatures and pressures. Therefore, giant stars have shorter lifespans compared to dwarf stars (like our Sun, which is a dwarf star and has a lifespan of about 10 billion years).
Thus, Statement-I is incorrect.
Giant stars are characterized by their large size and high luminosity. High luminosity is a direct consequence of a very high rate of nuclear fusion reactions occurring in their core or surrounding shells. This rapid burning of fuel is what causes them to expand and become giants. Dwarf stars, in contrast, have a much slower and more stable rate of nuclear reactions, which allows them to live longer.
Thus, Statement-II is correct.
Since Statement-I is incorrect, the question of whether Statement-II explains Statement-I becomes irrelevant in the context of options A and B. However, if Statement-I were correct, Statement-II (greater rate of nuclear reactions) would actually contradict a longer lifespan, as a higher reaction rate implies faster fuel consumption and thus a shorter life.
Statement-I is incorrect because giant stars, due to their higher mass and luminosity, consume their nuclear fuel much faster than dwarf stars, leading to shorter lifespans. Statement-II is correct because the immense luminosity and energy output of giant stars are a direct result of a significantly greater rate of nuclear reactions compared to dwarf stars. Therefore, Statement-I is incorrect, but Statement-II is correct.
The question asks to identify the first person to walk on the Moon. This is a direct factual recall question related to space exploration history.
The Apollo 11 mission, launched by NASA, successfully landed on the Moon on July 20, 1969. The crew consisted of Neil Armstrong, Buzz Aldrin, and Michael Collins. Neil Armstrong was the first human to step onto the lunar surface, followed by Buzz Aldrin.
Correct Option: D) Neil Armstrong
The question asks for the term used to describe a group of stars that form a recognizable shape. We need to identify the correct astronomical term from the given options.
Correct Option: C) Constellations — A constellation is a group of stars that form a recognizable pattern or outline in the night sky. Ancient civilizations often named these patterns after mythological figures, animals, or objects, such as Ursa Major (the Great Bear) or Orion (the Hunter).
The question asks for the alternative names of the constellation Ursa Major. We need to identify all commonly known names for this constellation.
Correct Option: D) All the above — Ursa Major is known by multiple names globally. "Great Bear" is its direct English translation. "Saptarishi" is its traditional Indian name, referring to seven prominent sages. "Big Dipper" is a well-known asterism within Ursa Major, often used interchangeably with the constellation itself due to its distinct shape.
The question asks to identify the first Indian woman to travel to space. This requires knowledge of prominent Indian-origin astronauts and their historical achievements in space exploration.
Kalpana Chawla was an American astronaut and engineer who was the first woman of Indian origin to go to space. She first flew on Space Shuttle Columbia in 1997.
A) Kalpana Chawla — Kalpana Chawla was indeed the first Indian-origin woman to go to space. She made her first space flight in 1997 aboard the Space Shuttle Columbia.
The question asks to identify which of the given options is NOT a planet of our Solar System. This requires knowledge of the planets in our Solar System and common celestial bodies.
Correct Option: B) Sirius is a star, not a planet in our Solar System.