The number of neutrons inside the nucleus of the element Uranium-235 is
- A.235
- B.92
- C.143
- D.51
Correct answer
Explanation
The correct answer is C, 143. The number 235 is the mass number and uranium's atomic number is 92, so the nucleus holds 235 minus 92, that is 143 neutrons. The mass number (A) counts protons and neutrons together, while the atomic number (Z) counts only protons, so neutrons = A − Z. Every uranium atom has 92 protons; its isotopes differ only in the number of neutrons. Uranium-235 makes up only about 0.7% of natural uranium, the rest being mostly U-238 with 146 neutrons. Yet U-235 is the isotope that splits easily when struck by a slow neutron, which is why reactor fuel is "enriched" in it. Option A is wrong because 235 is the total of protons and neutrons, not the neutrons alone. Option B is wrong because 92 is the number of protons, that is the atomic number. Option D is wrong because 51 has no link with this nucleus and is only a distractor. Exam tip: neutrons = mass number minus atomic number; U-235 has 143 and U-238 has 146.
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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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
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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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
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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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
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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