The correct answer is option 4: 1, 2 and 3.

Carbon sequestration involves capturing carbon dioxide (CO2) from the atmosphere or industrial processes and storing it in long-term reservoirs. This process helps to mitigate the impacts of anthropogenic CO2 emissions, which contribute to global warming and climate change. The following are potential sites for carbon sequestration:

1. Abandoned and uneconomic coal seams:

Coal seams are potential sites for carbon sequestration because they contain vast amounts of coalbed methane (CBM) that can be extracted for use as a fuel source, while simultaneously storing CO2 underground. CBM can be extracted by drilling into the coal seams and pumping out the methane. This process reduces the pressure in the coal seams, making it easier to store CO2 in the pores of the coal. Abandoned and uneconomic coal seams are ideal for carbon sequestration because they are no longer used for mining, and thus can be repurposed for this purpose.

2. Depleted oil and gas reservoirs:

Depleted oil and gas reservoirs can also be used for carbon sequestration. These reservoirs have already been drilled and produced, making them ideal for storing CO2. When oil or gas is extracted from a reservoir, the pressure in the reservoir decreases, making it suitable for CO2 storage. CO2 can be injected into the reservoir through existing wells, and it will displace the remaining oil or gas, which can be extracted and used as a fuel source. This process is known as enhanced oil recovery (EOR) and can be used to extract additional oil or gas while also storing CO2.

3. Subterranean deep saline formations:

Deep saline formations are porous rock formations that contain salty water deep underground. These formations are ideal for carbon sequestration because they are vast, secure, and can store large amounts of CO2. CO2 can be injected into the formations through wells drilled into the rock, and it will be stored in the pores of the rock, held in place by the salty water. Saline formations are considered a viable option for carbon sequestration because they are not suitable for other uses, such as agriculture or drinking water.

In conclusion, all three sites listed in the question - abandoned and uneconomic coal seams, depleted oil and gas reservoirs, and subterranean deep saline formations - can be used for carbon sequestration. However, it`s important to note that carbon sequestration is not a silver bullet for mitigating climate change and should be used in combination with other solutions, such as reducing emissions and transitioning to renewable energy sources.