UPSC CSE Prelims
Question 1
Which of the following adds/add nitrogen to the soil?
- Excretion of urea by animals
- Burning of coal by man
- Death of vegetation
Select the correct answer using the codes given below.
View correct answer and explanation
Correct answer: C
Correct Option: C
Explanation: Urea excreted by animals and the decomposition of dead vegetation return nitrogen compounds to the soil. Burning coal is not a normal biological source of soil nitrogen.
Statement/Pair-wise Analysis:
Statement/Item 1: Correct - Microbes convert animal urea into ammonium, adding available nitrogen to soil.
Statement/Item 2: Incorrect - Coal combustion releases nitrogen oxides to air; it does not directly enrich soil nitrogen in the intended nutrient-cycle sense.
Statement/Item 3: Correct - Decomposers mineralise nitrogen in dead plant matter, returning it to the soil.
Option-wise Analysis:
A: Incorrect - excludes true item 3.
B: Incorrect - includes false item 2 and excludes true item 1.
C: Correct - selects all and only the accurate statements/pairs.
D: Incorrect - includes false item 2.