A Mineral Called Montmorillonite Will Catalyze Some Interesting Reactions

A mineral called montmorillonite will catalyze some interesting reactions. The formula of one type of montmorillonite is NaCa₄(Si₂O₅) ₄F. If Na has a charge of +1, Ca has a charge of +2, and F has a charge of -1, what is the charge on each Si₂O₅ complex ion?

A) +2
B) +3
C) -2
D) +4
E) -4