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27-04-2018
Chemistry

contestada

How many neutrons are present in an atom of Sodium-20?
A. 12
B. 11
C. 10
D. 9

Respuesta :

mkryukova19 mkryukova19

05-05-2018

Mass number = atomic number(number of protons) + number of neutrons.

Sodium-20 - 20 is a mass number
Atomic number you need to find from the Periodic table. It is the ordinal number of the element.
Atomic number of Sodium (Na) is 11.
20=11+ number of protons
Number of neutrons is 20-11=9.
Correct answer D.9.

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