Consider the following statements : 1. The circulation of nitrogen from the inorganic compounds in the soil to form protein in plants and animals and back again is known as the nitrogen cycle. 2. The preparation of ammonia by Haber process is an endothermic reaction. 3. Urea is synthetically made by the action of ammonia and carbon dioxide under high temperature and high pressure. Which of the statements given above is/are not correct?
- A.1 and 3
- B.2 and 3
- C.2 only
- D.1 only
Correct answer
Explanation
The correct answer is C, 2 only. The Haber process is exothermic, not endothermic: nitrogen and hydrogen combine to form ammonia and release heat.
In the Haber process, N2 + 3H2 ⇌ 2NH3 gives out about 92 kJ for every two moles of ammonia formed. Because the forward reaction releases heat and reduces the number of gas molecules, a lower temperature and a high pressure push the equilibrium towards ammonia. In practice the plant runs at about 450°C and 200 atmospheres with an iron catalyst, a compromise between a good yield and a fast rate. Much of this ammonia is turned into urea, the most widely used nitrogen fertiliser in India.
Why the others are wrong: A, statement 1 correctly defines the nitrogen cycle and statement 3 correctly describes how urea is made, so neither is incorrect. B, statement 3 is correct, since urea comes from ammonia and carbon dioxide at high temperature and pressure. D, statement 1 is a correct definition, so it cannot be the incorrect one.
Exam tip: Haber process, exothermic, iron catalyst, about 450°C and 200 atm; NH3 + CO2 gives urea.
Practice Questions
View allWhich one of the following statements about xylem vessels in plants is not correct?
- A.Xylem vessels have lignified cell walls.
- B.Phloem sieve tubes are identical to xylem vessels in structure.
- C.Dead xylem vessels provide structural support to plants.
- D.Water is transported through xylem vessels.
Show answer
Phloem sieve tubes are not like xylem vessels: sieve tubes are living cells with thin walls and sieve plates, while mature xylem vessels are dead, hollow tubes with thick lignified walls.
Read the full explanation →Which one of the following effects best explains the high partial pressure of carbon dioxide causing haemoglobin to release oxygen in actively respiring tissues?
- A.Haldane effect
- B.Allee effect
- C.Bohr effect
- D.Eagle effect
Show answer
The Bohr effect is the fall in haemoglobin's affinity for oxygen when carbon dioxide and acidity rise, so oxygen is unloaded where tissues need it most.
Read the full explanation →Which one of the following statements about arteries is not correct?
- A.The inner lining is made of squamous endothelium.
- B.The middle layer is made of smooth muscle and elastic fibres.
- C.The outer layer is made of fibrous connective tissue with collagen fibres.
- D.Arteries have the thinnest walls amongst any other blood vessels.
Show answer
Arteries have the thickest walls of all blood vessels, not the thinnest, because they carry blood away from the heart under high pressure.
Read the full explanation →Which one of the following is not an exothermic reaction?
- A.Dissolution of calcium oxide in water
- B.Decomposition of vegetable matter into compost
- C.Decomposition of lead nitrate
- D.Dilution of sodium hydroxide with water
Show answer
Lead nitrate breaks down only when it is heated strongly, so the reaction absorbs heat and is endothermic. On heating, lead nitrate gives lead oxide, brown fumes of nitrogen dioxide and oxygen: 2Pb(NO3)2 → 2PbO + 4NO2 + O2.
Read the full explanation →Which of the following statements about a fluid at rest in a cup is/are correct? 1. Pressure is same at all the points in the fluid 2. Pressure is exerted on the walls. 3. Pressure exists everywhere in the fluid. Select the correct answer using the code given below :
- A.1 and 2 only
- B.2 and 3 only
- C.1 only
- D.1, 2 and 3
Show answer
A fluid at rest presses on the walls and has pressure at every point, but that pressure is not the same at all depths.
Read the full explanation →