Science & Technology MCQs for UPSC Prelims

Correct answer: A - Slow down the speed of neutrons

Heavy water (deuterium oxide) acts as a moderator in a nuclear reactor: it slows down fast neutrons to thermal speeds so they can efficiently cause further fission of uranium, which is option (a). Option (b) is the opposite of its role; it slows neutrons rather than speeding them up. Option (c) confuses the moderator with a coolant; although water can carry heat, the defining function of heavy water here is moderation. Option (d) describes the role of control rods (which absorb neutrons), not heavy water.

Correct answer: A - Digital security infrastructure

Public Key Infrastructure (PKI) is the framework of digital certificates, certifying authorities and public-private key pairs used to secure electronic transactions and authenticate identities, so it belongs to digital security infrastructure. It has nothing to do with food security, health-care and education, or telecommunication and transportation infrastructure. Therefore the correct context is digital security.

Correct answer: A - Nitric oxide

Nitric oxide is produced naturally in the human body and acts as a signalling molecule that relaxes the smooth muscle of blood vessel walls, causing vasodilation and increased blood flow, so option (a) is correct. Nitrous oxide is an anaesthetic and greenhouse gas, not a vasodilator synthesised for this role. Nitrogen dioxide and nitrogen pentoxide are toxic air pollutants, not physiological signalling molecules. Hence nitric oxide is the answer.

Correct answer: D - 1, 2 and 3

SaaS applications typically allow buyers to customise interfaces and configure data fields, so statement 1 is correct. Because the software is cloud-hosted, users can access their data from mobile devices anywhere, so statement 2 is correct. Web-based email services such as Outlook, Hotmail and Yahoo Mail are classic examples of SaaS, so statement 3 is correct. Hence all three are correct.

Correct answer: D - 1, 2 and 3

All three statements are correct. IceCube, at the Amundsen-Scott South Pole Station, instruments a full cubic kilometre of Antarctic ice with thousands of digital optical modules, making it the largest neutrino detector ever built. Its sensor strings are sunk between roughly 1450 and 2450 metres beneath the surface, so it is literally buried deep in the ice. Beyond detecting astrophysical neutrinos, it also functions as a telescope in the search for dark matter, looking for neutrino signatures that would result from dark matter particle annihilation. Hence 1, 2 and 3.

Correct answer: C - 1 and 3 only

Statements 1 and 3 are correct: vegetative propagation produces genetically identical clonal populations and can be carried out through most of the year. Statement 2 is wrong because ordinary vegetative propagation tends to transmit, not eliminate, viruses (virus elimination requires specialised meristem-tip culture). Hence 1 and 3 only.