<P> Soon after the accident, representatives from different activist groups arrived . The activists worked on organising the gas victims, which led to violent repression from the police and the government . </P> <P> Numerous actions have been performed: demonstrations, sit - ins, hunger strikes, marches combined with pamphlets, books, and articles . Every anniversary, actions are performed . Often these include marches around Old Bhopal, ending with burning an effigy of Warren Anderson . </P> <P> Cooperation with international NGOs including Pesticide Action Network UK and Greenpeace started soon after the tragedy . One of the earliest reports is the Trade Union report from ILO 1985 . </P> <P> In 1992, a session of the Permanent Peoples' Tribunal on Industrial Hazards and Human Rights took place in Bhopal, and in 1996, the "Charter on Industrial Hazards and Human Rights" was adopted . </P>

Leakage of which of the following gases had caused the bhopal gas tragedy