Headlines tell you what happened, but UPSC asks why. The UPSC Civil Services Examination, whether at the Prelims or Mains stage, increasingly rewards conceptual clarity and the ability to apply core ideas. That is especially true in the most dynamic areas of the syllabus: Science, Economy and Environment.The UPSC Weekly Concepts Snapshot brings you, every Wednesday, simplifies three important current themes from these subjects through an exam-oriented lens, focusing on concepts and clarity. Indian Express InfoGenIESCIENCEE85 fuel and flex-fuel vehicles (FFVs)Core Concept:— To understand E85, it is important to first know what Ethanol is. Ethyl alcohol, or Ethanol, is a liquid with several uses. At 95% purity, it is called rectified spirit and is used as the intoxicating ingredient in alcoholic beverages.— At 99%-plus purity, ethanol is used for blending with petrol. It is a common type of biofuel, a renewable fuel derived from biomass, from plants or agricultural, animal, domestic, and industrial biowaste.Story continues below this ad (Infographic AI-generated)— E85 is a high-ethanol blended fuel comprising 80-85% ethanol and 14-19% petrol, specifically designed for use in flex-fuel vehicles.— Regular petrol vehicles cannot use E85 as it is engineered exclusively for specialized flex-fuel vehicles. To push consumer adoption, the government has launched E85 at nearly Rs 20 per litre cheaper than normal petrol. What are Flex-fuel vehicles?— Flex-fuel vehicles are equipped with modified internal combustion engines that can run on petrol, ethanol, or any combination of the two without requiring manual adjustments by the driver. India’s first mass-market flex-fuel passenger carMaruti Suzuki India has launched the WagonR Flex Fuel billed as the country’s first mass-market flex-fuel passenger car, marking a significant step in India’s push towards alternative fuels. The car is capable of running on pure ethanol (E100), although it has been homologated to run on E85 fuel—85% ethanol and 15% petrol. — Sensors in the vehicle detect the fuel blend and automatically alter engine settings such as fuel injection and ignition timing to ensure optimal performance.Story continues below this ad— NITI Aayog officially classifies ethanol-based Flex-Fuel Vehicles (FFVs), including vehicles running on high ethanol blends such as E85, as Zero-Emission Vehicles.UPSC Twist Points: Butanol and ABE biofuels— Butanol and acetone-butanol-ethanol (ABE) mixtures as fuel are superior to ethanol. These products are synthesised naturally by solventogenic Clostridia – bacteria capable of fermenting a broad spectrum of cellulosic and hemicellulosic substrates. Among them, Clostridium beijerinckii BA101 has been identified as a particular butanol tolerant, high-yield strain. — However, ABE downstream processing for product recovery is more complex than a single product like ethanol, as the former involves separating multiple solvents (acetone-butanol-ethanol) while the latter needs water-ethanol separation. Researchers are also working on finding ways to make the ABE product recovery more viable. DON'T MISS | Knowledge Nugget: Why is natural gas discovery in Andaman basin making headlines?ECONOMYGovernment Securities (G-Secs)Core Concept: — G-secs are tradable instruments issued by the Central Government or the State Governments. It is used by the government to borrow money from the public. Story continues below this ad— The two key categories of G-Secs are treasury bills and dated securities. Treasury bills are short-term instruments which mature in 91 days, 182 days, or 364 days, and dated securities or government bonds are long-term instruments, which mature anywhere between 5 years and 40 years.— In 2010, the RBI introduced a new short-term instrument, known as Cash Management Bills (CMBs) with the aim to manage the temporary cash flow mismatches. CMBs, having the same generic character of T-Bills, are issued for maturities less than 91 days.— Treasury bills, or T bills are zero coupon securities and pay no interest. They are issued at a discount and redeemed at the face value at maturity. Let’s understand this through an example:A 91 day Treasury bill of ₹100 (face value) may be issued at say ₹ 98.20, that is, at a discount of say, ₹1.80 and would be redeemed at the face value of ₹100. The return to the investors is the difference between the maturity value or the face value (that is ₹100) and the issue price (that is ₹ 98.20).Story continues below this ad— According to the RBI, “In India, the Central Government issues both, treasury bills and bonds or dated securities while the State Governments issue only bonds or dated securities, which are called the State Development Loans (SDLs). G-Secs carry practically no risk of default and, hence, are called risk-free gilt-edged instruments.”— The RBI is the sole authority for the G-Secs which issues it through auctions. The auctions are conducted on an electronic platform called the E-Kuber, the Core Banking Solution (CBS) platform of RBI. — Commercial banks, Urban Co-operative Banks (UCBs), Insurance companies, and others who are members of E-Kuber can place their bids in the auction through this electronic platform.— Foreign investors can invest in Indian G-Secs through routes such as the General Route and the Fully Accessible Route (FAR). Story continues below this ad(i) General Route is the standard channel for foreign investors. It allows them to buy and sell permitted Indian G-secs, but comes with certain restrictions, such as caps on how much can be invested in a particular security, how long it must be held, and an overall investment limit. (ii) FAR is an open-access channel where foreign investors can invest in select G-Secs without restrictions that apply under the General Route.UPSC Twist Points: Bond yield — The effective interest on the government bonds is called yield. G-sec yields change over time; often several times during a single day. This happens because of the manner in which G-secs are structured.— Every G-sec has a face value, a coupon payment and price. The price of the bond may or may not be equal to the face value of the bond.Story continues below this ad— Here’s an example: Suppose the government floats a 10-year G-sec with a face value of Rs 100 and a coupon payment of Rs 5.If one were to buy this single G-sec from the government, it would mean that one will give Rs 100 to the government today and the government will promise to 1) return the sum of Rs 100 at the end of tenure (10 years), and 2) pay Rs 5 each year until the end of this tenure. At this point, the face value of this G-sec is equal to its price, and its yield (or the effective interest rate) is 5%. ENVIRONMENTEarthquakesCore Concept: — An earthquake is an intense shaking of the ground caused by movement under the earth’s surface. It happens when two blocks of the earth suddenly slip past one another, according to USGS. This releases stored-up ‘elastic strain’ energy in the form of seismic waves, which spreads through the earth and cause the shaking of the ground.Story continues below this ad In this photo provided by the Philippine Red Cross, rescuers inspect the damage after an earthquake in General Santos, Philippines. (Photo: AP)— The earth’s outermost surface, crust, is fragmented into tectonic plates. The edges of the plates are called plate boundaries, which are made up of faults. The tectonic plates constantly move at a slow pace, sliding past one another and bumping into each other. As the edges of the plates are quite rough, they get stuck with one another while the rest of the plate keeps moving.— Earthquake occurs when the plate has moved far enough and the edges unstick on one of the faults. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicentre.UPSC Twist Points: Earthquake Wave Types— When an earthquake occurs, it generates seismic waves that cause the shaking we experience. There are two major types of seismic waves: body waves and surface waves. Body waves comprise P and S waves, and they are called body waves because they can travel through the Earth’s interior, rather than being confined near the surface.— Primary or ‘P’ wave is a type of sound wave that travels through rock. In a P wave, the rock particles are alternately compressed and expanded, a process known as compressions and dilatations. This is why P waves are also referred to as compressional waves. They are capable of traveling through solids, liquids, and gases. Notably, P waves can move through the liquid outer core of the Earth.— In Secondary or ‘S’ wave, the rock particles slide past one another, which creates shear – hence, S waves are also known as shear waves. S waves cannot travel through liquids or gases, which means they do not propagate through the ocean or the outer core.— Surface waves are named for their tendency to be confined near the Earth’s surface, as opposed to traveling through the Earth’s interior like P and S waves. There are two main types of surface waves: Love waves, which are shear waves that are trapped near the surface, and Rayleigh waves, which exhibit particle motions similar to those of water particles in ocean waves.Prelims Practice MCQLet’s see how much can you recallConsider the following statements:1. E85 is a high-ethanol blended fuel designed for use in flex-fuel vehicles.2. Treasury Bills pay periodic coupon interest to investors during their tenure.3. S-waves cannot travel through liquids.Which of the statements given above is/are correct?(a) 1 only(b) 1 and 3 only(c) 1 and 2 only(d) 1, 2 and 3Answer Key (b)ALSO CHECKUPSC Prelims Weekly Snapshot: GPS interference, RBI’s Monetary Policy, HeatwavesUPSC Prelims Weekly Snapshot: Dimethyl Ether, CPI overhaul, Tar Balls UPSC Prelims Weekly Snapshot : Induction cooktop, Forex reserve, and Earth’s energy imbalance UPSC Prelims Weekly Snapshot: Talking cars, GDP rebasing and Nor’westers — quick look Click Here to read the UPSC Essentials magazine for May 2026. Share your views and suggestions in the comment box or at manas.srivastava@indianexpress.com Subscribe to our UPSC newsletter. Stay updated with the latest UPSC articles by joining our Telegram channel – Indian Express UPSC Hub, and follow us on Instagram and X.