The test solution is made basic and drops of 0.1 M Ca(NO3)2 are added but no precipitate forms. To what part of the experiment Procedure do you proceed? Solution procedure of adding Ca2+ to precipitates phosphates or carbonates before doint test for halides and sulphide. but since precipitate not formed means carbonates are not present so go for the test off halides( Cl- , Br-, I-)..