Which one of the following is not a monatomic element?
- A.Copper
- B.Helium
- C.Iodine
- D.Barium
Correct answer
Explanation
The correct answer is C, Iodine. Iodine exists as diatomic molecules, I₂, in which two iodine atoms share a pair of electrons; so its atomicity is two, not one.
Atomicity is the number of atoms in one molecule of an element. All the halogens, fluorine, chlorine, bromine and iodine, are diatomic, as are hydrogen, nitrogen and oxygen. Ozone (O₃) is triatomic, phosphorus (P₄) is tetra-atomic and sulphur (S₈) is polyatomic. Noble gases and metals are treated as monatomic, because their particles are single atoms; a metal's formula is written simply as Cu, Ba or Fe.
A is wrong because copper is a metal and is written as single atoms, Cu.
B is wrong because helium is a noble gas with a full outer shell, so its atoms stay single.
D is wrong because barium is an alkaline earth metal and is also treated as monatomic.
Exam tip: diatomic elements: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂; noble gases and metals are monatomic.
Practice Questions
View allThe potential difference between the terminals of an electrical heating device is 40 V, when it draws a current of 2 A from the source. Which one of the following is the correct value of current drawn by the heating device if the potential is increased to 140 V?
- A.7 A
- B.5 A
- C.4 A
- D.2 A
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By Ohm's law the heater's resistance is 40 V divided by 2 A, which is 20 ohms, so at 140 V it draws 140 divided by 20, or 7 A. Ohm's law states that, at constant temperature, the current through a conductor is directly proportional to the potential difference across…
Read the full explanation →Consider the following statements in the light of octane number and cetane number of fuels: 1. Cetane number is used for gasoline and octane number is used for diesel. 2. Octane number of n-hexadecane is 100 and cetane number of isooctane is 100. Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Both statements swap the two scales: octane number rates petrol, cetane number rates diesel, and their reference fuels are the other way round.
Read the full explanation →Which one among the following statements related to human eye is correct?
- A.For a person suffering from short-sight defect, the image of a distant object is focused behind the retina.
- B.Short-sight defect can be corrected by a converging spectacle lens.
- C.For a person suffering from long-sight defect, the image of a near object is focused behind the retina.
- D.Long-sight defect can be corrected by a diverging spectacle lens.
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In long-sightedness (hypermetropia) the eye cannot see nearby objects clearly because their image is formed behind the retina.
Read the full explanation →When sunlight (white light) falls on a triangular glass prism, a band of colours called a spectrum is obtained. Which one among the following represents this effect appropriately?
- A.Reflection
- B.Diffraction
- C.Refraction
- D.Dispersion
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The splitting of white light into its seven component colours by a prism is called dispersion. White light is a mixture of colours, and glass bends each colour by a different amount because its refractive index depends on wavelength.
Read the full explanation →Which one of the following statements is correct?
- A.The number of electrons in alpha particle is 2.
- B.The coordination number of EDTA is 6.
- C.The charge of beta (β) particle is +2.
- D.Both carbon and silicon form ionic compounds.
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EDTA is a hexadentate ligand: one EDTA ion binds a metal ion through six donor atoms, so it forms complexes with coordination number 6.
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