In the gamma decay of a nucleus
- A.the mass number of the nucleus changes whereas its atomic number does not change
- B.the mass number of the nucleus does not change whereas its atomic number changes
- C.both the mass number and the atomic number of the nucleus change
- D.neither the mass number nor the atomic number of the nucleus changes
Correct answer
Explanation
The correct answer is D, neither the mass number nor the atomic number of the nucleus changes. A gamma ray is a photon of energy with no mass and no charge, so emitting it leaves the count of protons and neutrons unchanged.
After an alpha or beta decay the new nucleus is often left in an excited state with extra energy. It drops to its ground state by giving out this energy as a gamma ray, a very high-frequency electromagnetic wave, much as an excited atom gives out light. The nucleus is the same element and isotope before and after; only its energy falls. Gamma rays are the most penetrating of the three radiations and need thick lead or concrete to stop them.
Option A is wrong because the mass number changes only in alpha decay, which removes two protons and two neutrons. Option B is wrong because a change in atomic number alone happens in beta decay. Option C is wrong because both numbers change together in alpha decay: mass number falls by 4 and atomic number by 2.
Exam tip: Alpha: A minus 4, Z minus 2; beta: Z plus 1; gamma: no change.
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…
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- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Read the full explanation →Which one among the following statements related to human eye is correct?
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- 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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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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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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