What is the aritmetric average of a set of data? And if you know is it mode?

The arithmetic average is the same as the mean. Add up all the numbers and divide by the number of numbers that you added.

The mode is the number that is repeated more often than any other. If you only have a short list in which no number appears more than once, there is no mode. There also can be more than one mode, as in a "bimodal distribution".