The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz).
What is the center frequency of channel 4?

What statement about 802.11 WLAN performance is true?

You are evaluating access points for use in the 5GHz frequency band.
What PHY supports this band and supports 80 MHz channels?

Two co-located 802.11b/g/n APs can interfere with one another and cause contention and collisions, even when the two APs are operating on non-overlapping channels (e.g. 1 & 6).
What deployment flaw could cause this problem?

You are using a tool that allows you to see signal strength for all APs in the area with a visual representation. It shows you SSIDs available and the security settings for each SSID. It allows you to filter by frequency band to see only 2.4 GHz networks or only 5 GHz networks. No additional features are available. What kind of application is described?