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Asked in PMC Practice Test 18 (2021) 2021

How many total number of electrons are present in 48 g of Mg2+? (NA = 6.023 x 10^23)

Correct answer: C. 20 NA

  • A. 24 NA
  • B. 2 NA
  • C. 20 NA
  • D. 1 NA

Explanation

The atomic number of magnesium is 12. Mg+2 means it has lost 2 electrons. Therefore, In the Mg+2 ion, there are 12-2 = 10 electrons. No. of moles = Mass / Molar mass = 48g / 24 g/mol = 2 mol 1 mol = NA Total number of electrons = No. of moles × No. of electrons per mole = 2 × NA × 10 = 20 NA This is numerical so it can only have one answer so option C is correct.

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About Moles and Avogadro's Number

The mole connects the microscopic number of particles with measurable mass, using Avogadro's number, 6.022 × 10²³ particles per mole. Questions involve molar mass, conversion between mass, moles and particles, percentage composition, empirical and molecular formulas, and distinguishing atoms, molecules, ions and formula units.

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