Test (Q). A compound X was fused with Na metal and the extract gave a white precipitate…

Test (Q). A compound X was fused with Na metal and the extract gave a white precipitate with AgNO₃. The Lassaigne’s extract gave a red colouration with neutral FeCl₃.
Test (R). While compound Y when fused with Na metal and subsequent analysis on its Lassaigne’s extract did not give any characteristic test.
Test (S). While compound Y on fusion with fusion mixture (sodium carbonate + potassium nitrate) or Na₂O₂, followed by extraction, followed by addition of Conc. HNO₃ and ammonium molybdate gave a yellow precipitate.
 
The formula of yellow precipitate is