Question

which element does not have the same number of electrons in its outermost shell as the other elements in its group? (1 point)
o boron (b)
o hydrogen (h)
o helium (he)
o bromine (br)

Explanation:

Step1: Recall group and valence electrons

Elements in a group have same number of valence (outermost shell) electrons. Helium (He) is a noble gas with 2 valence electrons (in its only shell, n=1). Other noble gases (like Ne, Ar) have 8 valence electrons (n≥2). Hydrogen (H) has 1, Boron (B) has 3, Bromine (Br) has 7 valence electrons. But Helium's group (noble gases) usually has 8 valence electrons (except He, which has 2 due to n=1). So He doesn't match the valence electron count of its group (noble gases) in terms of the "outermost shell electron count" pattern (others in group 18 have 8, He has 2).

Step2: Analyze each option

• Boron (B): Group 13, 3 valence electrons (consistent with group).
• Hydrogen (H): Group 1, 1 valence electron (consistent with group).
• Helium (He): Group 18, has 2 valence electrons (group 18 elements (except He) have 8; He's n=1 can hold max 2, but group trend is 8 for n≥2). So it doesn't have same outermost shell electron count pattern as others in group.
• Bromine (Br): Group 17, 7 valence electrons (consistent with group).

Answer:

Helium (He)