Answer : 4. "Hurdle"
Explanation :

Argument : an exchange of diverging or opposite views, typically a heated or angry one.
Frustration : the feeling of being upset or annoyed as a result of being unable to change or achieve something.
Advantage : a condition or circumstance that puts one in a favourable or superior position.
Fallout : the adverse results of a situation or action.
Hurdle : one of a series of upright frames over which athletes in a race must jump.
Stumbling Block : a circumstance that causes difficulty or hesitation.