Urea reacts with water to form A which will decompose to form B. B when passed through Cu²⁺ (aq), deep blue colour solution C is formed. What is the formula of C from the following?

Concept -

Decomposition of urea into the water -

⇒ Hydrolysis of urea does not cause dissociation of urea into water despite of that it forms ammonium carbonate (NH₄)₂CO₃. On heating, ammonium carbonate decomposes into carbon dioxide (CO₂), ammonia gas (NH3), and water.

When the ammonia gas evolved from the hydrolysis of water is passed through the deep blue colour solution of  Cu²⁺, a tetrahedrally coordinated copper complex ion [Cu(NH₃)₄]²⁺ with ammonia is formed.

Explanation - 

Step 1 - Reaction of urea with water gives ammonium carbonate (A).

Step 2 - Ammonium carbonate (A) on heating decomposes into ammonia gas (B) along with water and carbon dioxide.

Step 3 - When ammonia (B) passed through an aqueous solution of Cu²⁺, the formation of copper complex with ammonia i.e. tetraamminecopper(II) ion (C) takes place.

Chemical Reaction - 

So, (C) is [Cu(NH3)4]2+

Hence, the correct answer is option 4.