Answer: The statement they have one electron in the outermost electron shell. These are very active metals and easily lose their single valence electron, is true.
Step-by-step explanation:
Metals are the species which tend to lose electron(s) to acquire stable noble gas configuration.
Elements which tend to lose a single electron in order to acquire stability are active in nature because losing one electron is more easy as compared to losing two or more electrons.
For example, atomic number of sodium is 11 and its electronic distribution is 2, 8, 1.
Since, it contains only one valence electron and by losing it sodium will acquire stability. Hence, sodium is a very reactive metal.
Thus, we can conclude that the statement they have one electron in the outermost electron shell. These are very active metals and easily lose their single valence electron, is true.