1.  A Metal oxide soluble in excess caustic soda.
2. A metal chloride soluble in ammonium hydroxide solution.
3. A salt which gives ammonia gas when heated with NaOH.
4. A lead salt completely soluble in water.

Answers of your questions are as follow:

1. A metal oxide which is soluble in excess of caustic soda is aluminium oxide (Al₂O₃).

Al₂O₃ (s) + 2NaOH (aq)  + 3H₂O (l) → 2Na[Al(OH)₄] (aq)

2. The metal chloride which is soluble in ammonium hydroxide solution is silver chloride (AgCl).

AgCl(s) + 2NH₃(aq) → [Ag(NH₃)₂]⁺(aq) + Cl⁻(aq)

3. The salt which gives ammonia gas when heated with NaOH is ammonium chloride (NH₄Cl).

NH₄Cl  + NaOH  → NH₃ + NaCl  + H₂O

4. Lead nitrate, salt of lead is soluble in water.