Q80. Arrange the events chronologically:
1. Introduction of World Wide Web
2. Development of intercontinental ballistic missiles
3. Launch of the first communication satellite.
[UPSC NDA (II) 2025 – General Ability Test]
(A) 2 – 1 – 3
(B) 1 – 2 – 3
(C) 3 – 2 – 1
(D) 2 – 3 – 1
Answer: (D) 2 – 3 – 1
Explanation: Intercontinental ballistic missiles emerged during the 1950s. Early communications-satellite milestones came around the late 1950s and early 1960s. Tim Berners-Lee developed the World Wide Web much later, around 1989–1991, placing the events in order 2, 3, 1.
Q79. Which expression gives acceleration due to gravity at the surface of a spherical planet of mass M and radius R?
[RRB Group D, 11 December 2025, Shift 1]
(A) g = R/(GM²)
(B) g = GR/M²
(C) g = GM²/R
(D) g = GM/R²
Answer: (D) g = GM/R²
Explanation: Newton’s gravitational force on a body of mass m is GMm/R². Dividing that force by m gives the free-fall acceleration at the planetary surface, GM/R², when a roughly spherical mass distribution is assumed.
Q78. Statement I: Giant stars live much longer than dwarf stars.
Statement II: Giant stars have a greater rate of nuclear reactions than dwarf stars.
Which statement is correct?
[UPSC CSE Prelims 2024]
(A) Both are correct and II explains I
(B) Both are correct, but II does not explain I
(C) I is correct and II is incorrect
(D) I is incorrect and II is correct
Answer: (D) I is incorrect and II is correct
Explanation: Massive stars consume their nuclear fuel at a much faster rate despite having more fuel overall. Their higher luminosity therefore usually means shorter lifetimes than low-mass dwarf stars. The second statement is correct, but the claimed longevity is wrong.
Q77. Concerning the Square Kilometre Array (SKA), consider:
1. It is an international facility for an exceptionally sensitive radio telescope.
2. India has approved participation in the project.
Which is correct?
[UPSC NDA (I) 2024 – General Ability Test]
(A) 1 only
(B) 2 only
(C) Both 1 and 2
(D) Neither 1 nor 2
Answer: (C) Both 1 and 2
Explanation: SKA is a major international radio-astronomy project with antenna arrays in Australia and South Africa. India approved participation, strengthening its contribution to radio astronomy. It is designed to examine fundamental cosmic questions, including galaxy evolution and cosmic magnetism.
Q76. Who worked with Thomas Chamberlin in 1905 on a planetesimal explanation of the formation of the Solar System?
[SSC CPO Paper I, 27 June 2024, Shift 2]
(A) Inge Lehmann
(B) Forest Moulton
(C) Charles Lyell
(D) James Hutton
Answer: (B) Forest Moulton
Explanation: Forest Ray Moulton and Thomas Chrowder Chamberlin developed the Chamberlin–Moulton planetesimal hypothesis. It proposed that a close stellar encounter drew material from the Sun, subsequently forming small bodies. Modern models instead favour formation from a solar nebula.
Q75. Consider XPoSat:
1. It is India’s first dedicated polarimetry mission to study bright cosmic X-ray sources.
2. It carries two scientific payloads in low Earth orbit.
Which statements are correct?
[CGPSC Prelims, 11 February 2024 – General Studies]
(A) 1 only
(B) 2 only
(C) Both 1 and 2
(D) Neither 1 nor 2
Answer: (C) Both 1 and 2
Explanation: ISRO launched XPoSat to investigate polarisation of high-energy X-rays from astronomical sources including black-hole systems and neutron stars. Its two payloads, POLIX and XSPECT, provide complementary measurements from a low Earth orbit. Both statements are accurate.
Q74. Which pairs are correctly matched?
1. Cepheids — giant clouds of dust and gas
2. Nebulae — periodically brightening and dimming stars
3. Pulsars — neutron stars formed by collapse of massive stars.
How many are correct?
[UPSC CSE Prelims 2023]
(A) Only one
(B) Only two
(C) All three
(D) None
Answer: (A) Only one
Explanation: Cepheids are pulsating variable stars, while nebulae are clouds of gas and dust. Pulsars are rapidly rotating, magnetised neutron stars that produce observable periodic signals. Consequently, only the third identification is correctly paired.
Q73. Which of these countries has its own satellite-navigation system?
[UPSC CSE Prelims 2023]
(A) Australia
(B) Canada
(C) Israel
(D) Japan
Answer: (D) Japan
Explanation: Japan operates the Quasi-Zenith Satellite System, a regional navigation and augmentation constellation enhancing positioning over Japan and nearby areas. It complements other global navigation systems and can offer improved visibility in difficult urban and mountainous settings.
Q72. Which of the following was India’s first privately developed rocket launched in a mission facilitated by ISRO?
[UPSC NDA (I) 2023 – General Ability Test]
(A) Skyroot
(B) Prarambh
(C) Bazoomq
(D) Vikram-S
Answer: (D) Vikram-S
Explanation: Vikram-S was developed by Skyroot Aerospace and flew on the Prarambh mission in November 2022. Skyroot is the company, Prarambh the mission name, and Vikram-S the actual suborbital rocket. It was an important private-sector milestone.
Q71. Which is the correct descending order of density among Earth, Venus, Jupiter and Saturn?
[UPSC NDA (I) 2023 – General Ability Test]
(A) Earth > Jupiter > Venus > Saturn
(B) Jupiter > Earth > Saturn > Venus
(C) Earth > Venus > Jupiter > Saturn
(D) Earth > Venus > Saturn > Jupiter
Answer: (C) Earth > Venus > Jupiter > Saturn
Explanation: Earth and Venus are rocky and relatively dense, whereas Jupiter and Saturn are gas giants. Earth has the highest mean density of the four, followed by Venus. Jupiter is denser than Saturn, whose mean density is below water.
