Which of the following is not a poisonous indoor plant?

The spider plant is not considered a poisonous indoor plant, making it the correct answer. Spider plants (Chlorophytum comosum) are widely appreciated for their air-purifying qualities and are also safe for both children and pets. This characteristic makes them a popular choice for households and schools where safety is a priority.

In contrast, the other plants mentioned are known to be toxic. Philodendron contains calcium oxalate crystals, which can cause irritation and discomfort if ingested. Dieffenbachia, also called dumb cane, contains similar irritants that can lead to swelling and pain in the mouth and throat. Oleander is highly toxic and can be deadly if ingested, affecting the heart and causing serious health issues. Understanding the safe species to keep indoors is essential for minimizing risks in environments occupied by children or pets.