Multiple choice

The atomic mass of boron is 10.811. It contains 5 electrons. How many neutrons are present in it?

  1. 5

  2. 6.811

  3. 6

  4. 5.811
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C Correct answer
Explanation

The atomic mass is rounded off to give the mass number, which is 11. Mass number = Number of protons + Number of neutrons  Number of protons = Number of electrons = 5 So, the number of neutrons present in boron = Mass number - Number of protons = 11 - 5 = 6

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