(PLEASE HELP ASAP) In what ways can you determine the number of valence electrons in an atom
using the periodic table? (select all that apply)

The number of valence electrons equals the number in the ones place for groups 3-12

The number of valence electrons equals the number in the ones place for groups 1,2 and 13-18

The number of valence electrons equals the number in the tens place for groups 1,2and 13-18

The number of valence electrons equals the number in front of the "A" for groups 1A-80

Which statement is true if the refractive index of medium a is greater than that of medium b? a. total internal reflection is possible when light travels from air to medium b to medium a. b. total internal reflection is possible when light travels from medium a to medium b. c. total internal reflection is possible when light travels from medium b to medium a. d. total internal reflection is possible when light travels from air to medium a. e. total internal reflection is possible when light travels from air to medium b.