Question

​​​​​Why do in hno3 three gases combine to form a liquid

Answer 1

Only three gases will not form HNO3 with three gases water is used that's why we will get liquid HNO3 here is the explanation

The Ostwald process is a chemical process that in two stages, converts ammonia to nitric acid.

Formation of HNO3

The balanced equation for this reaction is different for each step:
Step 1:
4NH3 (gas) + 5O2 (gas) → 4NO (gas) + 6H2O (gas)
In this step, ammonia is heated with oxygen. This yields nitric oxide (NO) and water as products.

Step 2:
2NO (gas) + O2 (gas) → 2NO2 (gas)
In this step the nitric oxide (NO) that was created in the first is combined with oxygen again to create nitrogen dioxide (NO2).

Step 3:
3NO2 (gas) + H2O (liquid) → 2HNO3 (aqueous solution) + NO (gas)
In this step, the nitrogen dioxide is absorbed with water to create nitric acid (HNO3) as an aqueous solution. This also yields nitric oxide (NO).

Step 4:
4NO2 (gas) + O2 (gas) + 2H2O (liquid) → 4HNO3 (aqueous solution)
For this last step, the nitric oxide created along with the nitric acid is recycled and combined with oxygen and water to create a higher concentration of nitric acid (HNO3).