During a famous NASA experiment in 1989 researchers found that indoor plants can scrub the air of cancer-causing volatile organic compounds like formaldehyde and benzene. Later research found that soil microorganisms in potted plants also played a part in cleaning indoor air. Bill Wolverton, a former NASA research scientist who conducted the 1989 study stated "the amount of leaf surface area influences the rate of air purification." He stated that it's impossible to guess how many plants may be needed to clean a room of contaminants. But he would recommend at least two "good sized" plants per 100 sf. The bigger and leafier the plant, the better. Studies have also shown plants can reduce stress by calming the sympathetic nervous system. More research has sown spending time around nature and plants increases a persons mood and energy levels.
While Wolverton's first plant of choice for indoors would be the Golden Pothos here is a list of most common used house plants.