To solve this problem, we need to match the organisms in Column I with their corresponding processes in Column II. Let's analyze each organism:$\newline \bullet$a. Nitrococcus:$\newline$Nitrococcus is involved in the conversion of ammonia to nitrite.$\newline$This matches with (ii).$\newline \bullet$b. Rhizobium:$\newline$Rhizobium is known for the conversion of atmospheric nitrogen to ammonia.$\newline$This matches with (iv).$\newline \bullet$c. Thiobacillus:$\newline$Thiobacillus is involved in denitrification.$\newline$This matches with (i).$\newline \bullet$d. Nitrobacter:$\newline$Nitrobacter is responsible for the conversion of nitrite to nitrate.$\newline$This matches with (iii).$\newline$Now, let's match the items from Column I with Column II:$\newline a \rightarrow ii, b \rightarrow iv, c \rightarrow i, d \rightarrow iii \newline$This corresponds to Option 1.