Which one among the following is not a luminous object?
- A.Sun
- B.Proxima Centauri
- C.Jupiter
- D.Alpha Centauri
Correct answer
Explanation
The correct answer is C, Jupiter. Jupiter is a planet; it does not make its own light and shines only by reflecting sunlight.
A luminous object produces light of its own, as stars do by nuclear fusion in their cores, where hydrogen is turned into helium. Planets, moons and asteroids are non-luminous and are seen only because they reflect the light of a star. Jupiter is the largest planet of the solar system and one of the brightest objects in the night sky, which makes it look like a star, but its glow is reflected sunlight. It would need to be about 80 times more massive to begin fusion and become a star.
A is wrong: the Sun is a star and the main source of light and heat for Earth.
B is wrong: Proxima Centauri is a red dwarf star, the nearest star to the Sun at about 4.2 light years.
D is wrong: Alpha Centauri is a star system whose stars shine with their own light.
Exam tip: stars are luminous; planets and moons only reflect light. Nearest star after the Sun: Proxima Centauri.
Practice Questions
View allSyngamy results in formation of
- A.haploid zygote
- B.diploid zygote
- C.non-motile male gametes
- D.motile male gametes
Show answer
Syngamy is the fusion of a male and a female gamete, and since each gamete is haploid, their union gives a diploid zygote.
Read the full explanation →Human insulin molecule is composed of one α-chain having 21 amino acids and one β-chain having 30 amino acids. How many functional insulin genes occur in adult humans?
- A.One
- B.Two
- C.Three
- D.Four
Show answer
Humans have a single functional insulin gene, INS, on the short arm of chromosome 11, and both chains of insulin come from it.
Read the full explanation →Which one of the following is the value of one nanometer?
- A.10⁻⁷ cm
- B.10⁻⁶ cm
- C.10⁻⁴ cm
- D.10⁻³ cm
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One nanometre is 10⁻⁹ metre, and since one metre is 100 (10²) centimetres, it equals 10⁻⁷ centimetre. The prefix nano means one billionth.
Read the full explanation →Which of the following is the general formula for saturated hydrocarbons?
- A.CₙH₂ₙ₊₂
- B.CₙH₂ₙ₋₂
- C.CₙH₂ₙ₊₁
- D.CₙH₂ₙ₋₁
Show answer
Saturated open-chain hydrocarbons are the alkanes, and every alkane fits the formula CₙH₂ₙ₊₂. In a saturated hydrocarbon every carbon atom is joined to others only by single bonds, so each carbon holds the largest possible number of hydrogen atoms.
Read the full explanation →Which one of the following is not an epidemic disease?
- A.Cholera
- B.Malaria
- C.Smallpox
- D.Elephantiasis
Show answer
Elephantiasis, or lymphatic filariasis, is an endemic disease: it stays steadily present in certain regions and develops slowly over years, rather than breaking out suddenly in a large number of people.
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