Hydrochlorofluorocarbons (HCFCs), replacement for chlorofluorocarbons (CFCs),…

Concept. The Montreal Protocol never bans an ozone-depleting substance on a single global date. For each family of chemicals it fixes a stepped timetable of consumption and production cuts that ends in a zero-consumption date, and it runs two such timetables in parallel — one for non-Article 5 (developed) parties and one for Article 5 (developing) parties, which are given extra time. HCFCs sit inside this framework as transitional substitutes: they still carry chlorine and therefore still deplete ozone, only far less than CFCs do, which is why the Protocol gave them an accelerated ladder of their own rather than a permanent place. On that HCFC ladder — and this feature belongs to the HCFC schedules, not to every controlled chemical family — each of the two zero dates is followed by a narrow servicing-only exemption running ten further years, so that equipment already installed can still be maintained.

Application. Decision XIX/6, the 2007 Montreal adjustment, accelerated the HCFC ladder for both party classes. Reading the two schedules side by side gives the year the question asks for:

Now read the two rows together. The developed-country schedule reaches its zero date in 2020, and the 0.5%-a-year servicing exemption that follows it expires in 2030. The developing-country schedule — the one India follows — reaches its zero date in 2030. The same year therefore closes both sides of the ladder: it removes the developed countries' last permitted servicing quantity and it is the date from which developing-country HCFC consumption is set at zero.

HCFCs therefore have to be phased out completely by 2030.

Cross-check. What survives past 2030 under the control schedule is not unrestricted HCFC use but a narrow exemption sitting above the zero limit — production and consumption capped at an average of 2.5% a year for Article 5 parties — restricted to servicing refrigeration and air-conditioning equipment installed before 1 January 2030, and that exemption itself expires in 2040. This is why some secondary tables render the Article 5 rungs as "97.5% in 2030, 100% in 2040", and why the word "completely" gives 2040 a literal basis. The date fixed by the control schedule itself, and the year carried by the official NTA answer key for this paper, is 2030; 2040 only closes the servicing tail that follows it.

Contrast. The remaining years belong elsewhere in the treaty timetable:

• 2025 — the 67.5% consumption cut, the last reduction rung before the Article 5 zero date, not that date itself.

• 2035 — a mid-decade date here belongs to the Kigali Amendment, which phases down hydrofluorocarbons (HFCs): Article 5 Group 1 parties hold HFC consumption 30% below baseline from 2035. HFCs contain no chlorine, so they warm the climate without depleting ozone — a different control regime altogether.