Arrange the given alkoxides in order of their decreasing basic strengths.
Dear Student, These are the conjugate bases of the given acids.
It means that strongest is the acid least basic will be its conjugate base.
So third one is the strongest acid because it has less number of electron releasing groups attached to it so less electron density on the carbon atom and easy removal of the electrons so its conjugate base will be least basic.
Hence the order of there decreasing basic strength is same as that is given in the question.