Reaction between magnesium ribbon and lemon juice

magnesium ribbon dissolves and colourless gas bubbles evolved.

Chemical equation:
Mg + 2CH3COOH → (CH3COO)2Mg + H2

Ionic equation:
Mg(s) + 2H (aq) → Mg2 (aq) + H2(g)

lemon juice contains citric acid C6H8O7, which has 3 ionizable H+ ion. Colorless gas bubble(hydrogen) will be produced when Mg is put into lemon juice.