What are the different characteristics between 802.11 b, a, g, and n

What are the different characteristics between 802.11 b, a, g, and n? Choose three random people and ask them what type of phone/tablet they have. Get the model number. Then, determine what type of Wi-Fi compatibility exists on that device.

What Wi-Fi router/access point devices should you choose to handle the greatest number of people with the largest security? Explain the rationale behind your choice.