Consider the following statements : 1. Packaged foods are purged with nitrogen gas in order to prevent their oxidation. 2. Tooth decay starts when pH of the mouth is lower than 5.5. 3. The reactivity of metals decreases in the order : Mg > Fe > Zn. Which of the statements given above is/are not correct ?
- A.2 and 3
- B.1 and 3
- C.1 and 2
- D.3 only
Correct answer
Explanation
The correct answer is D, 3 only. Statements 1 and 2 are correct; statement 3 is wrong because zinc is more reactive than iron.
In the reactivity series the order is K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au, so the correct sequence is Mg > Zn > Fe. This is why zinc displaces iron from iron sulphate solution, and why a zinc coating protects iron in galvanisation. Statement 1 is true: chips packets are filled with nitrogen, an unreactive gas, to keep oxygen away and stop the oils from turning rancid. Statement 2 is true: when bacteria turn sugar into acid and the mouth's pH falls below about 5.5, tooth enamel starts to dissolve.
A is wrong: statement 2 is correct, so it should not be among those marked not correct.
B is wrong: statement 1 is correct, since nitrogen flushing prevents oxidation.
C is wrong: statements 1 and 2 are the correct ones; only 3 is not.
Exam tip: reactivity Mg > Al > Zn > Fe; enamel decays below pH 5.5; chips packets use nitrogen against rancidity.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
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- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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