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An isotope of an element, atomic number z, has mass number 2z + 4. How manyneutrons are...

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roshan-rox | Valedictorian

Posted May 14, 2013 at 2:38 PM via web

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An isotope of an element, atomic number z, has mass number 2z + 4. How many
neutrons are in the nucleus of the element?
A) z + 4

B) z + 2

C) z

D) 4

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Top Answer

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jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted May 14, 2013 at 3:05 PM (Answer #1)

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We know that mass number of an atom is the sum of protons and neutrons inside the atom. Usually this is expressed in unified atomic mass units or 1/12 of the mass of a single C-12 (carbon-12) atom at rest.

Isotope means an atom which has same number of electrons but different neutrons.

atomic mass number `= N_p+N_n`

`2z+4 = z+N_n`

`N_n = 2z+4-z = z+4`

So there will be (z+4) neutrons in the isotope.


So the correct answer is A)

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