Black plastics are basically not recyclable due to their color. They can also contain unregulated amounts of toxic chemicals including heavy metals and flame retardants which means they could be hazardous to your health.
Plastic #5 is also microwave safe. Its full name is polypropylene and it's commonly used as food containers, spoons, and forks. It has a melting point of 0 to 250 degrees, which is why this is perfect for those microwave meals.