Which of the following is/are true
A. Multiplicity in `Fe^(3+)` is greater that that in `Co^(3+)`
B. `Ti^(3+), Cr^(+), SC^(2+)` ions are diamagnetic .
C. Value of `(n+l+m)` for last electron of Mg is 3.
D. The value of `Z_("eff")` for 3s electron of Cl is 10.9