ANS:B - 3.5:1

In the steam reforming process of naphtha to produce hydrogen, the usual ratio of steam to carbon (S:C) maintained is typically around 3.5:1. This ratio ensures efficient conversion of the hydrocarbons in naphtha to hydrogen and carbon monoxide via the following endothermic reaction: CH4+H2O→CO+3H2CH4​+H2​O→CO+3H2​ Maintaining a higher ratio of steam to carbon is essential to promote the desired conversion reactions and maximize the yield of hydrogen while minimizing the formation of undesirable by-products like carbon dioxide. Therefore, a ratio of around 3.5:1 is commonly employed in the steam reforming process of naphtha for hydrogen production in the nitrogenous fertilizer industry.