What is achievement of Dobereiner's law of traids?

1 What are the merits and demerits of newland's classification? 2 X and Y are two elements having which have similar properties and obey Newland's land of octaves. How many elements are there in-between X and Y? 4 Lithium, Sodium and potassium were put in the same group on the basis of their similar properties.
i) What is the similarity in their properties? 5 State two reasons for rejecting law of octaves.