Environmental Chemistry: JEE Advanced PYQ, 2007–2026

Q1 · Chemistry · Environmental Chemistry

In modern dry cleaning, liquid carbon dioxide with a suitable surfactant is used in place of which solvent?

• ATetrachloroethene
• BBenzene
• CAcetone
• DDiethyl ether

Q2 · Chemistry · Environmental Chemistry

CF₂Cl₂ reaches the stratosphere and is exposed to short-wavelength UV radiation there. Which initial photochemical step releases the ozone-depleting species?

• ACF₂Cl₂ + hν → •CF₂Cl + Cl•, because the C–Cl bond is weaker than the C–F bond.
• BCF₂Cl₂ + hν → •CFCl₂ + F•, because fluorine is the most electronegative atom and leaves most readily.
• CCF₂Cl₂ + hν → CF₂ + Cl₂, because both chlorines leave together as a molecule.
• DCF₂Cl₂ + hν → CCl₂ + F₂, because the two fluorine atoms are lost as a stable molecule.

Q3 · Chemistry · Environmental Chemistry

In the stratosphere, ozone absorbs ultraviolet radiation (O₃ + hν → O₂ + O), and the oxygen atoms then re-form ozone (O + O₂ + M → O₃ + M), releasing the energy as heat. Which pair of consequences correctly follows if the stratospheric ozone concentration falls substantially?

• AMore UV-B reaches the Earth's surface, and the stratosphere becomes cooler because less UV energy is absorbed and converted to heat.
• BMore UV-B reaches the Earth's surface, and the stratosphere becomes warmer because the extra UV that is not blocked heats the upper air.
• CLess UV-B reaches the Earth's surface, because ozone depletion products such as ClO• also absorb UV-B strongly, and the stratosphere cools.
• DMore UV-B reaches the Earth's surface, but the stratospheric temperature is unchanged because ozone destruction and re-formation cancel in their heat effects.

Q4 · Chemistry · Environmental Chemistry

Which green chemistry principle is most directly served by carrying out a chemical process at room temperature and atmospheric pressure instead of at high temperature and high pressure?

• AEnergy efficiency, because less energy is needed to heat, pressurise and maintain the process
• BAtom economy, because milder conditions increase the fraction of reactant atoms that end up in the product
• CUse of renewable feedstock, because room-temperature processes use natural raw materials
• DBiodegradability of the product, because mild conditions make the product break down faster

Q5 · Chemistry · Environmental Chemistry

A person sleeping in a closed room with a coal fire can die from CO poisoning even though the air in the room still contains about 20% oxygen. Which statement best explains this?

• ACO binds to the iron of haemoglobin to form carboxyhaemoglobin, which is far more stable than oxyhaemoglobin, so even a low concentration of CO blocks the transport of oxygen to tissues.
• BCO dissolves in blood to form carbonic acid, which sharply lowers blood pH and denatures haemoglobin.
• CCO oxidises Fe(II) in haemoglobin to Fe(III), forming methaemoglobin that cannot carry oxygen.
• DCO produced by the fire displaces the oxygen of the room air so that the oxygen fraction falls too low to breathe.

Q6 · Chemistry · Environmental Chemistry

N2 and O2 make up about 99% of dry air but are not greenhouse gases, whereas CO2, a linear and nonpolar molecule, is one. Which of the following gives the correct reason?

• AA vibration absorbs infrared radiation only if it changes the dipole moment of the molecule. The only vibration of N2 or O2 does not, whereas the bending and asymmetric stretching vibrations of CO2 do.
• BCO2 absorbs infrared radiation because the bent shape of the molecule gives it a permanent dipole moment, which N2 and O2 lack.
• CNonpolar molecules cannot absorb infrared radiation. N2 and O2 are nonpolar, and CO2 is an exception only because of its polar C=O bonds.
• DThe bond dissociation energies of N≡N and O=O are so high that infrared photons cannot excite these molecules, whereas the C=O bonds of CO2 are weak enough for IR to break them.

Q7 · Chemistry · Environmental Chemistry

In green chemistry, which of the following is used as a safer solvent for dry cleaning in place of tetrachloroethene (perchloroethylene)?

• ASupercritical carbon dioxide
• BLiquid chlorofluorocarbon (CFC-113)
• CCarbon tetrachloride
• DBenzene

Q8 · Chemistry · Environmental Chemistry

In the stratosphere, ozone absorbs UV radiation by O₃ + hν → O₂ + O. The oxygen atom then recombines with O₂ in the presence of a third body M: O + O₂ + M → O₃ + M. Taken together, which statement correctly describes the effect of this pair of reactions?

• AThere is no net change in ozone; the absorbed UV energy is converted to heat, which warms the stratosphere.
• BOzone is permanently destroyed, because the photolysis step removes one O₃ molecule each time a photon is absorbed.
• CThere is a net gain of ozone, because every absorbed photon produces one O atom that goes on to form a new O₃ molecule.
• DThe absorbed UV energy is stored as chemical energy in the O₃ formed, so the stratosphere is not heated.

Q9 · Chemistry · Environmental Chemistry

Ethane is prepared by the Wurtz reaction: 2CH3Br + 2Na → C2H6 + 2NaBr. A student obtains the maximum possible ethane, a 100% yield, and claims that the process is therefore perfectly efficient in the green-chemistry sense. Using atom economy = (mass of desired product ÷ total mass of reactants in the balanced equation) × 100, which statement is correct? (H = 1, C = 12, Na = 23, Br = 80)

• AThe atom economy is 100%, because a 100% yield means every reactant atom ends up in the desired product.
• BThe atom economy is about 15.8%, because 30 g of ethane is formed from 190 g of CH3Br.
• CThe atom economy is about 22.6%, because 30 g of ethane is formed alongside 103 g of NaBr.
• DThe atom economy is about 12.7%, so most of the reactant mass ends up as NaBr waste even at 100% yield.

Q10 · Chemistry · Environmental Chemistry

Which step of the Chapman mechanism directly forms ozone molecules in the stratosphere?

• AO2 + hν → O + O
• BO + O2 + M → O3 + M
• CO3 + hν → O + O2
• DO3 + O → 2O2