Threshhold frequency is defined as the minimum light frequency necessary to start photo-electric emission from the surface. This frequency is just effecient enough to emit electrons without any additional force or energy. this minimum frequency creates the necessary result that is sought by the person. The photo electric emission for certain metals can occir with threshhold frequency. The importance of this threshhold frequency lies in the fact that this has been used to create numerous instruments like amplifiers for use of people.
The answer would be B. An example of this would be the Noble gasses. They include: Helium, Argon, Neon, and so on. They are all located on the very right side because they share similar chemical behaviours; they dont react very easily because they have a full valence shell.
