3. Black Tie Optional or Formal
A black tie optional event usually means formal. Men may choose a dark suit or tuxedo, with a white dress shirt and conservative tie of solid color or classic pattern. Leather dress shoes would be the suggestion here.
For women, a floor-length gown or cocktail dress is a good choice, as are formal separates such as a silk blouse and chiffon skirt. A dressy pant suit would also be appropriate.