Quality of air we breathe has become a huge cause of concern and yet most of the focus seems to be on external sources of air pollution. Indoor pollution that kills millions around the world remains a silent killer, as most people tend to feel safe in the confines of their homes or workplace. One of the easy ways to tackle indoor air pollution are plants. Here are 5 houseplants that purify the air around you, act as a green shield against toxins and make for an ideal gift.