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The mass number of an element is 18. It ...

The mass number of an element is 18. It contains 7 electrons. What is the number of protons and neutrons in it ? What is the atomic number of the element ?

Text Solution

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Mass number 18 = number of protons + number of neutrons.
Number of protons = number of electrons in a neutral atom = 7
`therefore` Number of protons = 7 = atomic number
and number of neutrons = mass number - number of protons (or electrons)
= 18 - 7 = 11
Therefore, the number of protons is 8, number of neutrons is 11, and the atomic number is 7.
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