The correct answer is option 1: an agreement among the participants over CO2 emission. The Copenhagen Summit for Climate Change in 2009 was a significant event where leaders from around the world gathered to discuss and address the issue of global climate change. The main objective of the summit was to negotiate a global agreement to reduce greenhouse gas emissions and combat climate change.

Option 1 correctly states that an agreement was reached among the participants regarding CO2 emissions. This agreement is known as the Copenhagen Accord. However, it is important to note that the Copenhagen Accord did not set legally binding emission reduction targets. Instead, it outlined the commitment of the participating countries to limit global warming to below 2 degrees Celsius. The accord also established a framework for developed countries to provide financial support to developing countries for climate change adaptation and mitigation efforts.

Options 2, 3, and 4 are not correct. There was no unanimity of views among the developed and BASIC bloc of countries, nor did the African countries unite as a bloc during the summit. Additionally, the acceptance of the US as a leader to attain the objective of the Copenhagen Summit is not mentioned or relevant to the outcome of the event.