High density is the most likely answer
Answer:
Number of valence electrons stays the same
I don’t have a periodic table nearby but I believe the answer is C, iron.
1 — Element D and A ( Which are Sodium and aluminium )
2 — ( 2 + 8 + 3 = 13 electrons total ) Element A Because it's atomic number is 13.
3 — Element E Is stable. ( Which is Argon )
( Note, Elements which has 8 election on its outermost cell is stable. ( Helium is exception which is a noble gas but have 2 electrons in outermost cell )
4 — Element F , which is hydrogen. ( Hydrogen is the only element to not have any neutron )
5 — Element D ( Which is sodium )
6 — The element F ( Which is hydrogen ) Don't contain any neutron.
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