A magnesium ribbon is burnt in oxygen to give a white compound ' X ' accompanied by the emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound ' Y '. The balanced chemical equation when ' X ' is dissolved in water will be- 

A white chemical called magnesium oxide, orMgO, is created when a magnesium ribbon burns in oxygen along with the emission of light. Magnesium oxide so makes up the chemical "X." 
The magnesium nitride Mg3N2 is created when a burning magnesium ribbon is exposed to a nitrogen environment. Consequently, magnesium nitride is compound "Y." Magnesium hydroxide is created when the white compound magnesium oxide, MgO, dissolves in water. 
MgO+H2O →Mg(OH)2