The vertical side member of a shutter frame, is known A. Style B. Reveal C. Mullion D. Post

Style
Reveal
Mullion
Post

The correct answer is: Mullion.

A mullion is a vertical structural member that divides a window or door opening into smaller panes or lights. It is typically made of wood, metal, or stone, and is often decoratively carved or molded.

A style is a vertical member that supports the lintel of a door or window opening. It is typically made of wood or stone, and is often decorated with moldings or carvings.

A reveal is the exposed area of a wall between the frame of a door or window and the surrounding wall. It is typically painted or stained to match the wall.

A post is a vertical structural member that supports a beam or lintel. It is typically made of wood, metal, or stone, and is often square or rectangular in shape.