GATE 2021 ES – Previous Year Questions with Solutions
All 65 questions of GATE 2021 ES with answers and explanations. Read each question, then practise it by topic or as a full paper.
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- Question 1 – A city currently has population 1102500, increasing at 5% per annum. What was its population two years ago?
- Question 2 – Positive integers p, q satisfy p/q+q/p=3. Find p2/q2+q2/p2.
- Question 3 – Find the least number of squares to add to the shown arrangement so P–Q becomes a line of symmetry.
- Question 4 – Nostalgia is to anticipation as is to . Choose the analogous relation.
- Question 5 – Which sentences are grammatically correct? (i) I woke up from sleep. (ii) I woked up from sleep. (iii) I was woken up from sleep. (iv) I was wokened…
- Question 6 – Statements: all purple are green; all black are green. Conclusions: I some black are purple; II no black is purple. Which option is logically correct?
- Question 7 – Computers are ubiquitous and improve efficiency from agriculture to space exploration. Artificial intelligence enables computers to learn given enough…
- Question 8 – A square sheet of side 1 unit is cut along its main diagonal. One resulting triangle is revolved about a short edge to form a solid cone. Find cone…
- Question 9 – The bar chart shows minutes X and Y exercise each day of a week. On how many days does one student exercise at least 10% longer than the other?
- Question 10 – Corners are cut from an equilateral triangle to produce the shown regular convex hexagon. Find hexagon area/original triangle area.
- Question 11 – Find slope of the tangent to y=x² at(x, y)=(3,9).
- Question 12 – Evaluate x0x2/ x.
- Question 13 – Powdered-coal samples have(mass kg, carbon wt%):(2,88),(1,90),(2,80),(1,90). Find carbon weight percentage of the completely mixed sample.
- Question 14 – An air sample has 30 ppmv CO at 25°C in the morning. The same sample is analysed at 35°C later. What is its CO concentration in ppmv?
- Question 15 – In fluid statics, the buoyant-force line of action always passes through .
- Question 16 – Choose integrated waste-management priority from highest to lowest.
- Question 17 – For aquifer saturated thickness d, hydraulic conductivity K and transmissivity T, which relation holds?
- Question 18 – What is the terminal electron acceptor in aerobic respiration?
- Question 19 – What drives Type-I settling in a sedimentation tank?
- Question 20 – For RMS sound pressure p and reference hearing-threshold pressure p₀,which formula gives sound pressure level in dB?
- Question 21 – The product-life diagram shows material extraction→production→distribution→use→end of life. Scope P covers production only, Q extraction through…
- Question 22 – At the1992 Rio UN Conference on Environment and Development, which principle supports mitigation of serious or irreversible environmental threats…
- Question 23 – Rank municipal-waste components from greatest to least biodegradability.
- Question 24 – A 10 kg moisture-free sample loses6 kg when heated950°C without air, and 7 kg at the same temperature with air. Find fixed-carbon percentage.
- Question 25 – Among the listed pH values, where is chlorine most effective as a water disinfectant?
- Question 26 – Find nitrogen oxidation states in NH₄⁺,NO₂⁻ and NO, respectively.
- Question 27 – Water has H⁺ concentration10 mg/L. Hydrogen atomic mass1 g/mol. Find pH.
- Question 28 – Which nucleotide pairing is present in double-helical DNA?
- Question 29 – Which substances are both greenhouse gases and ozone-depleting substances?
- Question 30 – For dependent y and independent x, classify dy/dx=x2y.
- Question 31 – Which listed values solve x3-10x2+31x-30=0?
- Question 32 – Which quantities are represented in a wind rose?
- Question 33 – A flocculation tank has velocity gradient800 s⁻¹,volume 40 m³,water viscosity9×10⁻⁴ N s/m². Find theoretical mixing power in kW, rounded to an…
- Question 34 – A culture grows from 5×10⁴ to 1280×10⁴ cells/mL by binary fission with no deaths. Find number of generations as an integer.
- Question 35 – A 4 cm diameter orifice produces a 3.5 cm jet diameter at vena contracta. Velocity coefficient .98. Find discharge coefficient, to two decimals.
- Question 36 – P+Q=pmatrix3&1\\2&12pmatrix and P-Q=pmatrix-1&-7\\8&2pmatrix. Find Q.
- Question 37 – A biased die has faces k=1,…,6 with P(k) proportional to k². Find probability of an even result.
- Question 38 – Match P diffusion, Q drag force, R atmospheric stability to i Pasquill, ii Fick, iii Stokes.
- Question 39 – Match P Ramsar Convention, Q Kyoto Protocol, R Basel Convention, S Montreal Protocol to i ozone depletion, ii transboundary hazardous waste, iii…
- Question 40 – Ideal PFR and CFSTR treat a pollutant by first-order kinetics at the same inlet concentration, flow and target outlet concentration. Which comparison…
- Question 41 – A 200 mL sample atpH9 requires 25 mL of .02 N H₂SO₄ to reachpH4.5. Find total alkalinity in mg/L as NaHCO₃. Atomic masses Na23,H1,C12,O16,S32,Ca40.
- Question 42 – An STP treats20000 m³/day with 200 mg/L suspended solids. Primary clarification removes60% into sludge containing5 wt% solids, density1000 kg/m³. Find…
- Question 43 – Match P trommel, Q magnetic separator, R hammer mill, S eddy-current separator to i size reduction, ii aluminium separation, iii screening, iv ferrous…
- Question 44 – Water containsNa⁺92,K⁺19.5,Ca²⁺40,Mg²⁺24 mg/L. Atomic masses Na23,K39,Ca40,Mg24. Find SAR for irrigation assessment.
- Question 45 – Select correct statements about Nitrobacter nitrifying bacteria.
- Question 46 – Which are dominant removal mechanisms for spherical particles below 10 µm in a fabric filter?
- Question 47 – Which are primary air pollutants?
- Question 48 – Select correct statements about glycolysis.
- Question 49 – For conventional water-quality MPN testing, select correct statements.
- Question 50 – At a fixed location, which influence solar radiation incident on a rooftop solar-water heater?
- Question 51 – f(x)+3f(g(x))=x-2,where g(x)=(3x+1)/(x-3). Find f(5)/f(8) as an integer.
- Question 52 – Function y satisfies y-y=0,y→1 as x→−∞,and y(0)=2. Find y(0) as an integer.
- Question 53 – At NTP298 K,1 atm, air contains .30 ppmv NO₂. One mole ideal gas occupies24.45 L;NO₂ molar mass46 g/mol. Find NO₂ concentration in µg/m³,rounded to an…
- Question 54 – A 10 m wide rectangular channel carries20 m³/s at 1 m depth. Using g=10 m/s²,find specific energy in m, to one decimal.
- Question 55 – Two pipes A, B in series have equal length and Darcy friction factor. B has twice A’s internal diameter. Ignore minor losses. Find h A/h B as an…
- Question 56 – A permeable formation has porosity20%,hydraulic gradient2%,and actual seepage velocity .0025 m/s. Assume laminar flow. Find hydraulic conductivity K…
- Question 57 – A leaking waste tank maintains .5 mg/L contaminant. A well is 2 km away;effective travel speed .4 m/day. First-order contaminant half-life10 years.…
- Question 58 – A manufacturing unit earns net profit Rs.6000/year for 15 years. Discount rate 8%/year. Find net present worth of these profits in rupees, as an…
- Question 59 – A 900 mm sewer on slope .004 carries .15 m³/s. Manning n=.013. Find actual/full-flow discharge ratio, to two decimals. Use π=3.14.
- Question 60 – A 10 MLD activated-sludge plant receives primary-treated sewage BOD₅140 mg/L into a 1500 m³ aeration tank. MLVSS3000 mg/L;effluent BOD₅5 mg/L. Find…
- Question 61 – A 100000-person community produces2.5 kg MSW/person/day. Landfill area 12×10⁴ m²,available depth 25 m including cover. Compacted waste density800…
- Question 62 – A stationary-container collection truck spends .1 h unloading each container, two containers per location, and .2 h travelling between locations.…
- Question 63 – Water containsNa⁺ .25 M, Ca²⁺ .12 M, Cl⁻ .32 M, HCO₃⁻ .05 M. Find ionic strength in M, to two decimals.
- Question 64 – Excess solid CaSO₄ is added to pure water atpH7,with undissolved solid remaining. Ksp=2.1×10⁻⁵ mol²/L². Find equilibrium sulfate concentration in…
- Question 65 – Two completely mixed facultative sewage ponds are in series, each HRT6 days. Overall BOD₅ reduction90%. Both have the same first-order rate constant.…