Answer
a) $K$; b) $F$; c) $Ar$; d) $Sr$; e) $Zn$; f) $Nb$
Work Step by Step
a. An alkali metal in period 4
Element: Potassium (K)
Group 1A (alkali metals), Period 4
b. A second-row element in group 7A
Element: Fluorine (F)
Group 7A (halogens), Period 2
c. A noble gas in the third period
Element: Argon (Ar)
Group 8A (noble gases), Period 3
d. A main group element in period 5 and group 2A
Element: Strontium (Sr)
Group 2A (alkaline earth metals), Period 5
e. A transition metal in group 12, period 4
Element: Zinc (Zn)
Group 12, Period 4
f. A transition metal in group 5, period 5
Element: Niobium (Nb)
Group 5, Period 5.
