The correct option is B 4NH3+5O2→4NO+6H2O
The balanced chemical equation involved in manufacturing of HNO3 by Ostwald's process are shown as:
Step 1 Formation of nitric oxide (NO)
4NH3(g)+5O2(g)Pt/Rh, gases~ catalyst−−−−−−−−−−−−−→500K, 9bar4NO(g)+6H2O
Step 2 Formation of nitrogen dioxide (NO2)
2NO(g)+O2(g)→2NO2(g)
Step 3 Absorption of NO2 (Formation of HNO3)
3NO2(g)+H2O→2HNO3(l)+NO(g)
Therefore, the correct option is (b).