Which one of the following statements is correct?
- A.The oxidation number for hydrogen is always zero.
- B.The oxidation number for hydrogen is always +1.
- C.The oxidation number for hydrogen is always -1.
- D.Hydrogen can have more than one oxidation number.
Correct answer
Explanation
The correct answer is D, Hydrogen can have more than one oxidation number. Hydrogen shows 0, +1 or -1 depending on what it is bonded to.
In the free element H2 its oxidation number is 0, as for every element in its uncombined state. When it combines with non-metals that are more electronegative than itself, as in water (H2O), hydrogen chloride (HCl) or ammonia (NH3), it is +1. When it combines with very electropositive metals such as sodium, potassium, lithium or calcium, it forms ionic hydrides like NaH and CaH2, where it carries a charge of -1. This dual behaviour is one reason hydrogen's position in the periodic table is debated: it resembles the alkali metals in forming H+ and the halogens in forming H-.
A is wrong because hydrogen is zero only in H2. B is wrong because in metal hydrides it is -1, so +1 is not always true. C is wrong because in most compounds, such as water and acids, it is +1.
Exam tip: hydrogen = 0 in H2, +1 with non-metals, -1 in metal hydrides like NaH and LiAlH4.
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.
Read the full explanation →Which one of the following statements is correct?
- 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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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- 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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