<p>The <strong>UPSC Civil Services Preliminary Examination 2026</strong> is slated for <strong>24 May 2026</strong>. With only a few weeks left, candidates should shift from gathering new material to a focused revision of high‑impact science and technology (S&T) topics that have featured in recent current‑affairs. These topics are repeatedly asked in GS‑3 and often intersect with GS‑1 (environment), GS‑2 (policy) and GS‑4 (ethics). A smart, selective review will help you consolidate facts, understand concepts and save valuable time.</p>
<h3>Key Topics for Revision</h3>
<ul>
<li><span class="key-term" data-definition="Sodium‑ion battery — A rechargeable battery that uses sodium ions instead of lithium, offering lower cost and safety advantages; important for India's energy transition (GS3: Science & Technology)">Sodium‑ion battery</span>: Abundant, cheaper than lithium, can be extracted from seawater, operates at zero‑volt transport, uses aluminium conductors and tolerates higher temperatures.</li>
<li><span class="key-term" data-definition="Reverse osmosis — A desalination technique that forces seawater through a semi‑permeable membrane to produce fresh water; crucial for water‑security strategies (GS3: Science & Technology)">Reverse osmosis</span>: Energy‑intensive, generates CO₂ emissions and brine waste; used for desalination, water‑reuse in pharma, biotech and radioactive waste treatment.</li>
<li><span class="key-term" data-definition="Helioseismology — The study of solar interior by observing surface oscillations, similar to seismology for Earth; relevant for space research (GS3: Science & Technology)">Helioseismology</span>: NASA’s Solar Dynamics Observatory and its Helioseismic and Magnetic Imager track solar oscillations to map internal solar movements.</li>
<li><span class="key-term" data-definition="Critical minerals — Minerals such as lithium, nickel, cobalt, rare‑earth elements that are essential for batteries, renewable energy and defence; a strategic resource for India (GS3: Science & Technology)">Critical minerals</span>: Include lithium, nickel, cobalt, manganese, graphite for batteries and rare‑earths for wind‑turbine magnets; also aluminium and copper for electricity networks.</li>
<li><span class="key-term" data-definition="CAR T‑cell therapy — An advanced cancer treatment that engineers a patient’s T‑cells to target tumour cells; reflects progress in biotechnology (GS3: Science & Technology)">CAR T‑cell therapy</span>: Reprograms T‑cells with chimeric antigen receptors to hunt blood cancers such as leukaemia and lymphoma.</li>
<li><span class="key-term" data-definition="Oort Cloud — A distant spherical shell of icy bodies surrounding the Sun up to 100,000 AU; important for understanding comet origins (GS3: Science & Technology)">Oort Cloud</span>: Ice debris extending up to 1.6 light‑years; source of long‑period comets and marks the Sun’s gravitational boundary.</li>
<li><span class="key-term" data-definition="Vehicle‑to‑Vehi
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