Q50. Which planet is closest to the Sun?
[SSC JE, 23 March 2021, Morning]
(A) Neptune
(B) Mercury
(C) Mars
(D) Venus
Answer: (B) Mercury
Explanation: Mercury occupies the innermost planetary orbit, completing a revolution around the Sun in about 88 Earth days. Despite being closest to the Sun, it is not the hottest planet; Venus has a denser greenhouse atmosphere.
Q49. Which frequency band is not normally used for INSAT/GSAT satellite communication?
[RPSC RAS Prelims, 27 October 2021]
(A) Ka band
(B) C band
(C) MF band
(D) Ku band
Answer: (C) MF band
Explanation: Communication satellites commonly use microwave bands such as C, Ku and Ka for reliable, high-capacity links. The medium-frequency (MF) band is much lower in frequency and is associated mainly with terrestrial services such as AM broadcasting.
Q48. Which project employs three spacecraft in an equilateral triangle with sides approximately one million kilometres long and laser beams exchanged between them?
[UPSC CSE Prelims 2020]
(A) Voyager 2
(B) New Horizons
(C) LISA Pathfinder
(D) Evolved LISA
Answer: (D) Evolved LISA
Explanation: The evolved Laser Interferometer Space Antenna concept uses precisely measured laser links between widely separated spacecraft to detect gravitational waves. Its immense baseline is suited to low-frequency waves from massive cosmic systems that ground-based observatories cannot easily access.
Q47. What are the four planets nearest the Sun collectively called?
[UPSC CDS (II) 2020 – General Knowledge]
(A) Terrestrial planets
(B) Giant planets
(C) Dwarf planets
(D) Gas planets
Answer: (A) Terrestrial planets
Explanation: Mercury, Venus, Earth and Mars are terrestrial planets, built mainly from rock and metal and possessing relatively solid surfaces. Jupiter, Saturn, Uranus and Neptune are larger outer planets with thick gaseous layers.
Q46. Which solar-system statements are correct?
I. Mercury is the hottest planet.
II. Ganymede is Saturn’s largest moon.
III. Neptune has extremely cold methane-rich atmospheric features.
IV. Phobos and Deimos orbit Mars.
[CGPSC Civil Services Prelims 2020 – Paper I]
(A) I and II only
(B) II and III only
(C) III and IV only
(D) All four
Answer: (C) III and IV only
Explanation: Venus, not Mercury, has the highest average surface temperature because of its runaway greenhouse atmosphere. Ganymede is Jupiter’s moon, not Saturn’s. Neptune contains atmospheric methane, while Phobos and Deimos are the two small Martian moons.
Q45. Which was the first Arab nation to launch a mission to Mars in July 2020?
[UPPSC Civil Services Prelims 2020 – General Studies I]
(A) Saudi Arabia
(B) Kuwait
(C) United Arab Emirates
(D) Qatar
Answer: (C) United Arab Emirates
Explanation: The United Arab Emirates launched the Hope orbiter, also called Al-Amal, toward Mars in July 2020. The probe was intended to study the Martian atmosphere and weather patterns and marked the first interplanetary mission by an Arab nation.
Q44. For the Northern Hemisphere, which date-event pairs are conventionally correct?
1. Winter solstice — 22 December
2. Autumn equinox — 23 September
3. Summer solstice — 21 June
4. Spring equinox — 21 March.
[WBCS Prelims 2020]
(A) 1 and 2 only
(B) 2 and 3 only
(C) 3 and 4 only
(D) All are conventionally matched
Answer: (D) All are conventionally matched
Explanation: Solstices occur when the Sun reaches its extreme apparent north–south positions; equinoxes occur when the Sun crosses the celestial equator. Exact dates can shift by a day depending on year and time zone, but the listed dates are standard textbook approximations.
Q43. What was the significance of detecting the merger of massive black holes billions of light-years away?
[UPSC CSE Prelims 2019]
(A) Detection of Higgs bosons
(B) Detection of gravitational waves
(C) Confirmation of intergalactic wormhole travel
(D) Proof of the exact nature of singularities
Answer: (B) Detection of gravitational waves
Explanation: Merging black holes radiate gravitational waves, ripples in spacetime predicted by general relativity. Their detection opened a new way to observe cosmic events that may emit little or no ordinary light and test strong-gravity physics.
Q42. For which measurements can satellite images or remote-sensing data be used? 1. Vegetation chlorophyll 2. Greenhouse-gas emissions from rice fields 3. Land-surface temperature.
[UPSC CSE Prelims 2019]
(A) 1 only
(B) 2 and 3 only
(C) 3 only
(D) 1, 2 and 3
Answer: (D) 1, 2 and 3
Explanation: Remote sensing uses recorded radiation in different spectral bands to infer vegetation condition, surface temperature and certain atmospheric trace-gas patterns. Combining satellite measurements with models and ground observations also supports estimates of agricultural greenhouse-gas emissions.
Q41. Which planet has the least mass among Neptune, Jupiter, Mars and Mercury?
[UPSC CDS (I) 2019 – General Knowledge]
(A) Neptune
(B) Jupiter
(C) Mars
(D) Mercury
Answer: (D) Mercury
Explanation: Mercury has the smallest mass of any of the eight major planets. Jupiter and Neptune are giant planets, and Mars is considerably more massive than Mercury. Mercury remains dense because of its unusually large metallic core.
