How many days it generally takes to convert urea into nitrate form?

Correct option is B

The conversion of urea to nitrate (NO₃⁻) in the soil is a two-step microbial process:
Urea → Ammonium (NH₄⁺) via the enzyme urease
Ammonium → Nitrite → Nitrate through nitrification, carried out by nitrifying bacteria like Nitrosomonas and Nitrobacter.
Under optimal soil conditions (good moisture, temperature, aeration), this transformation typically takes about 7 days.
However, factors like cold temperatures or compacted soils may slow the process.
(a) About 3 days – ❌ Too short; ammonium may form but full nitrification not complete.
(b) About 7 days – ✅ Approximate time under favorable conditions – correct answer.
(c) About 15 days – ❌ Could happen under less ideal conditions, but not typical.
(d) About 20 days – ❌ Delayed conversion happens in poor soil conditions or low microbial activity.