How many of the given compounds will give a positive Biuret...

The biuret test, also known as Piotrowski's test, is a chemical test used for detecting the presence of peptide bonds. The Biuret reagent is made of sodium hydroxide ($NaOH$) and hydrated copper(II) sulfate, together with potassium sodium tartrate, the latter of which is added to chelate and thus stabilize the cupric ions. The reaction of the cupric ions with the nitrogen atoms involved in peptide bonds leads to the displacement of the peptide hydrogen atoms under the alkaline conditions.

So, among the given options tripeptide and Glycylalanine will have peptide bond, so it will show Biuret test.