Answer:
LiBr
Step-by-step explanation:
Group 1 metals give a characteristic colour when subjected to flame test. The colour can tell us exactly what the identity of metal being studied.
Now, Lithium metal gives a red flame. Hence the group 1 metal ion is Li^+. Similarly, bromides give a creamy precipitate when reacted with silver nitrate.
This means that the solid substance under study is LiBr.