Can it ever happen in a wings level flight that the Turn and Slip indicator ball is to the full right/left? If so then when and what will be the flight path of such an aircraft? Thanks in advance.
Yes, when the rudder is highly deflected. The slip indicator gives us information on the yaw axis of the airplane and "level flight" is generally in relation to a neutral pitch and power situation (i.e. not climbing or descending). An aircraft can be yawed with rudder input alone and subsequently cause the slip ball to deflect as appropriate.