A soft silver-white metal (A) burns with a golden-yellow flame to give a yellow powder (B) which on treatment with water liberates oxygen giving a clear solution (C). The solution, when mixed with Al, attacks the metal, liberating a gas (D) and forming a water-soluble compound (E). The metal (A) dissolves in liquid NH3 to form a deep blue solution which is a good conductor and an excellent reducing agent. Identify (D):