Which angles form an adjacent pair? a. < 3 and < 4b. < 1 and < 3c. < 1 and < 4d. < 2 and < 4

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8