Q.Identify the correct statement i. Sulphur is essential for amino acids Cystine and Methionine
ii. Low level of N, K, S and Mo affect the cell division
iii. Non-leguminous plant Alnus which contain bacterium Frankia
iv. Denitrification carried out by nitrosomonas and nitrobacter.

Step 1. Statement I says sulphur is essential for the amino acids cystine and methionine - this matches the chapter directly, since sulphur is described as an essential component of cystine, cysteine and methionine, so statement I is true.

Step 2. Statement III says the non-leguminous plant Alnus contains the bacterium Frankia - this also matches the chapter directly (Alnus and Casuarina are named as non-legume hosts of Frankia), so statement III is true.

Step 3. Statement IV says denitrification is carried out by Nitrosomonas and Nitrobacter - this is false: those two bacteria carry out nitrification (ammonia to nitrite to nitrate), while denitrification (nitrate back to atmospheric N2) is carried out by a different set of bacteria, Pseudomonas, Thiobacillus and Bacillus subtilis. …

Check each statement against the chapter's stated facts, then use the fact that the answer choices only offer prefix combinations (I; I+II; I+II+III; all four) …

• Confusing nitrification (Nitrosomonas, Nitrobacter) with denitrification (Pseudomonas, Thiobacillus, Bacillus subtilis). …