4. Which is TRUE about period or series?
a. Period 1 has two elements corresponding to the number of electrons
b. Periods 1 and 2 each has eight elements corresponding to the eight electrons
C. Period 4 and 5 each has 18 elements corresponding to 18 elements
d. Period 7 includes 14 elements which were placed at the upper part of the
table to form the actinide series​