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Chemistry MCQs

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21
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What is the term for the amount of energy required to remove an electron from an atom?

  • A Electron affinity
  • B Ionization energy
  • C Electronegativity
  • D Bond energy
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Correct Answer: Option B — Ionization energy
Explanation: Ionization energy is the minimum energy required to remove an electron from a gaseous atom or ion. It generally increases across a period and decreases down a group in the periodic table due to atomic structure.
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22
Hard nts Uploaded: 06 Aug 2026

What is the oxidation state of oxygen in most compounds?

  • A -2
  • B -1
  • C +1
  • D +2
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Correct Answer: Option A — -2
Explanation: Oxygen typically has an oxidation state of -2 in most of its compounds, as it tends to gain two electrons to complete its outer shell. Exceptions include peroxides, where oxygen has an oxidation state of -1.
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23
Hard pms Uploaded: 06 Aug 2026

Which of the following elements is a metalloid?

  • A Silicon
  • B Sodium
  • C Sulfur
  • D Silver
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Correct Answer: Option A — Silicon
Explanation: Silicon is classified as a metalloid because it exhibits properties intermediate between metals and nonmetals. It is widely used in the electronics industry as a semiconductor material for computer chips and solar panels.
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24
Hard css fpsc ppsc Uploaded: 14 Jul 2026

What is the term for the energy required to remove one electron from a gaseous atom?

  • A Electron affinity
  • B Electronegativity
  • C Lattice energy
  • D Ionisation energy
Permalink
Correct Answer: Option D — Ionisation energy
Explanation: Ionisation energy is the minimum energy required to remove one electron from a gaseous atom in its ground state with first ionisation energy increasing across a period and decreasing down a group.
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25
Hard css fpsc ppsc Uploaded: 14 Jul 2026

Which element has the highest electronegativity on the Pauling scale?

  • A Oxygen
  • B Chlorine
  • C Nitrogen
  • D Fluorine
Permalink
Correct Answer: Option D — Fluorine
Explanation: Fluorine has the highest electronegativity of all elements at 3.98 on the Pauling scale due to its small atomic size and high effective nuclear charge on its outer electrons.
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26
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Which of the following best describes Avogadro's number?

  • A 6.022 x 10^20
  • B 6.022 x 10^23
  • C 6.022 x 10^26
  • D 6.022 x 10^29
Permalink
Correct Answer: Option B — 6.022 x 10^23
Explanation: Avogadro's number, 6.022 x 10^23, represents the number of particles present in one mole of any substance. This fundamental constant bridges the gap between atomic-scale quantities and measurable macroscopic amounts of matter.
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27
Hard css fpsc ppsc Uploaded: 14 Jul 2026

What is the chemical formula for potassium permanganate a strong oxidising agent?

  • A KMnO4
  • B K2MnO4
  • C K2SO4
  • D K2Cr2O7
Permalink
Correct Answer: Option A — KMnO4
Explanation: Potassium permanganate has the formula KMnO4 and is a strong oxidising agent used in water treatment as a disinfectant and in analytical chemistry as a titrating agent.
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28
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Which scientist proposed the modern periodic law?

  • A Antoine Lavoisier
  • B John Dalton
  • C Dmitri Mendeleev
  • D Henry Moseley
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Correct Answer: Option D — Henry Moseley
Explanation: Henry Moseley formulated the modern periodic law based on atomic number rather than atomic mass, which Mendeleev had originally used. Moseley's X-ray spectroscopy work corrected several anomalies in Mendeleev's original table.
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29
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Which element has the highest melting point among all elements?

  • A Iron
  • B Tungsten
  • C Platinum
  • D Osmium
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Correct Answer: Option B — Tungsten
Explanation: Tungsten has the highest melting point of any element at approximately 3422°C, making it valuable for applications requiring extreme heat resistance such as light bulb filaments and welding electrodes.
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30
Hard css fpsc Uploaded: 14 Jul 2026

What is the chemical formula for chloroform a once common anaesthetic?

  • A CH2Cl2
  • B CCl4
  • C CHCl2
  • D CHCl3
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Correct Answer: Option D — CHCl3
Explanation: Chloroform has the chemical formula CHCl3 and was historically used as an anaesthetic and is now used as a solvent in chemical synthesis and laboratory work.
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31
Hard css fpsc ppsc Uploaded: 14 Jul 2026

What are the products of the electrolysis of brine sodium chloride solution?

  • A Sodium and water
  • B Hydrogen chlorine and sodium hydroxide
  • C Chlorine and sodium
  • D Sodium chloride and water
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Correct Answer: Option B — Hydrogen chlorine and sodium hydroxide
Explanation: Electrolysis of brine produces hydrogen gas at the cathode chlorine gas at the anode and sodium hydroxide solution remaining in the electrolyte through the chlor-alkali process.
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32
Hard nts Uploaded: 06 Aug 2026

What is the term for elements with the same number of protons but different numbers of neutrons?

  • A Allotropes
  • B Isomers
  • C Isobars
  • D Isotopes
Permalink
Correct Answer: Option D — Isotopes
Explanation: Isotopes are variants of an element that share the same atomic number but differ in mass number due to varying neutron counts. Carbon-12 and Carbon-14 are common examples of isotopes used in dating and research.
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33
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What is the chemical formula for bleaching powder used in water purification?

  • A Ca(OH)2
  • B CaCO3
  • C Ca(OCl)Cl
  • D CaCl2
Permalink
Correct Answer: Option C — Ca(OCl)Cl
Explanation: Bleaching powder is calcium hypochlorite chloride Ca(OCl)Cl made by passing chlorine gas over slaked lime and used as a disinfectant and bleaching agent.
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