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T cells and B cells are similar because they both deal with fighting of viruses.
D. Two electrons in its first energy level; eight electrons in its second energy level; six valence electrons in its outermost energy level.
Please correct me if I'm wrong!! :)
Reactivity trends of halogen:
1) Melting point and boiling points increased down the
group
2) Colour becomes darker.
E.g. Fluorine (pale yellow)
Chlorine (yellowish-green)
Bromine (reddish-brown)
Iodine (purplish-black)
Astatine (black)
3) The reactivity decreases down the group.
Reactivity:
F > Cl > Br > I > At
