Which of the following methods is effective for removing heavy metals from water?

Reverse osmosis is an effective method for removing heavy metals from water due to its ability to separate contaminants at a molecular level. In this process, water is forced through a semi-permeable membrane that allows only water molecules to pass through, while blocking larger contaminants including heavy metals such as lead, mercury, and cadmium. This method is highly efficient and can reduce concentrations of various heavy metals to very low levels, making it a popular choice for water purification in both industrial and domestic settings.

Filtration, while useful for removing larger particles and certain contaminants, is not typically effective against dissolved heavy metals because the sizes of the metal ions are smaller than the filter pores. Coagulation involves the addition of chemicals to water to aggregate contaminants into large clusters that can then be removed, but it may not effectively remove all heavy metals and often requires subsequent filtration or sedimentation. Boiling water can kill bacteria and viruses but does not remove heavy metals; in fact, boiling can concentrate the metals as water evaporates.

Thus, reverse osmosis stands out as the most effective method for removing heavy metals from water due to its specific targeting of dissolved contaminants through a physical barrier.