Which one of the following statements with regard to ozone is not correct?
- (a)Ozone is found mostly at 15-55 km in the atmosphere.
- (b)Ozone is produced by gaseous chemical reactions.
- (c)16th November is celebrated as the International Day for the Preservation of the Ozone Layer.
- (d)Ozone is a form of oxygen in which three oxygen atoms are bounded together.
Correct — C, 16th November is celebrated as the International Day for the Preservation of the Ozone Layer. That is the false statement, and the date is the giveaway. The day is 16 September, not 16 November. The United Nations General Assembly fixed it by resolution 49/114 in 1994, choosing the anniversary of the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer at Montreal on 16 September 1987. Nothing about ozone attaches to 16 November. The other three statements describe ozone accurately enough for the paper's purposes: it is concentrated high in the atmosphere, it is made and destroyed by gas-phase photochemical reactions, and it is the three-atom form of oxygen.
- (a)Ozone is found mostly at 15-55 km in the atmosphere. — Treated as correct by the key. Stratospheric ozone is the bulk of atmospheric ozone and the layer is usually given as 15 to 35 km, with the peak concentration near 20 to 25 km; the paper's upper figure of 55 km is generous but still describes the stratosphere and above, not the surface.
- (b)Ozone is produced by gaseous chemical reactions. — Correct as stated. Ultraviolet light splits an oxygen molecule into two free atoms, and each free atom joins another oxygen molecule to make ozone — the Chapman cycle, entirely a set of reactions among gases.
- (d)Ozone is a form of oxygen in which three oxygen atoms are bounded together. — Correct in substance. Ozone is O3, an allotrope of oxygen with three atoms in the molecule against the two of ordinary O2.
Ozone is O3, an allotrope of oxygen. In the stratosphere it forms a thin shield that absorbs essentially all incoming ultraviolet-C and most ultraviolet-B, which is why it matters for life at the surface. Near the ground the same molecule is a pollutant and a component of photochemical smog. Column ozone is measured in Dobson Units. Chlorofluorocarbons release chlorine atoms in the stratosphere that destroy ozone catalytically, a link established by Molina and Rowland in 1974 and recognised with the 1995 Nobel Prize in Chemistry shared with Paul Crutzen.
Date items like this are decided in seconds if the anchor is stored with the date rather than the date alone. Ozone Day is 16 September because the Montreal Protocol was signed on 16 September 1987. Keep it apart from World Environment Day on 5 June, which marks the 1972 Stockholm Conference, and from World Water Day on 22 March. One printed detail is worth noticing: option (d) says the three oxygen atoms are 'bounded' together, where the word wanted is bonded. That is the booklet's own slip and it does not change what is being tested. The treaty regime has since worked — the Antarctic ozone hole is shrinking and the layer is judged to be on a recovery path, while the 2016 Kigali Amendment extended the protocol to hydrofluorocarbons, which do not deplete ozone but are potent greenhouse gases.
- The International Day for the Preservation of the Ozone Layer is 16 September, set by UN General Assembly resolution 49/114 in 1994.
- The date marks the signing of the Montreal Protocol on 16 September 1987; the protocol entered into force on 1 January 1989.
- The Vienna Convention for the Protection of the Ozone Layer, its framework treaty, was signed on 22 March 1985.
- The ozone layer sits in the stratosphere, conventionally 15 to 35 km, and absorbs all UV-C and most UV-B.
- The Kigali Amendment of 2016 added a phase-down of hydrofluorocarbons, which harm the climate rather than the ozone layer.
Store the anniversary with the date and the wrong month stops being memorisable at all.
- Mixing the ozone treaties with the climate treaties — Kyoto and Paris have nothing to do with ozone depletion.
- Treating HFCs as ozone-depleting; they are covered by Kigali because they are greenhouse gases.
- Forgetting that ozone at ground level is a pollutant, so 'ozone is harmful' and 'ozone is protective' are both true in their own layers.
As a not-correct statement item like this one, as a plain date question, or as a matching item pairing observances with their dates.
Which one of the following is associated with the issue of control and phasing out of the use of ozone-depleting substances?
- (a) Bretton Woods Conference
- (b) Montreal Protocol
- (c) Kyoto Protocol
- (d) Nagoya Protocol
Answer(b) Montreal Protocol
Names the treaty whose signing date is the whole point of this CDS item. Once the Montreal Protocol is fixed to 16 September 1987, the false statement here identifies itself.
The formation of ozone hole in the Antarctic region has been a cause of concern. What could be the reason for the formation of this hole?
- (a) Presence of prominent tropospheric turbulence; and inflow of chlorofluorocarbons
- (b) Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons
- (c) Absence of polar front and stratospheric clouds; and inflow of methane and chlorofluorocarbons
- (d) Increased temperature at polar region due to global warming
Answer(b) Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons
The chemistry behind the treaty. It explains why chlorine from CFCs destroys stratospheric ozone fastest over Antarctica in spring, which is the science the Montreal Protocol was written to answer.
Ozone layer, which absorbs the ultra-violet radiation, is found in which one of the following layers of the atmosphere?
- (a) Ionosphere
- (b) Troposphere
- (c) Mesosphere
- (d) Stratosphere
Answer(d) Stratosphere
Tests the altitude claim that statement (a) of this question makes. The layer is stratospheric, which is why a figure in the tens of kilometres is acceptable and a figure near the ground would not be.
- practice — not a real PYQ
The International Day for the Preservation of the Ozone Layer is observed on which one of the following dates?
- (a)16 September
- (b)5 June
- (c)22 March
- (d)5 December
Answer(a) 16 September — the anniversary of the signing of the Montreal Protocol in 1987.
- practice — not a real PYQ
The Kigali Amendment of 2016 to the Montreal Protocol provides for the phase-down of which one of the following?
- (a)Chlorofluorocarbons
- (b)Hydrofluorocarbons
- (c)Halons
- (d)Carbon tetrachloride
Answer(b) Hydrofluorocarbons — they do not deplete ozone at all, but they are powerful greenhouse gases, which is why the amendment was needed.