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2. A beryllium atom has 4 protons, 5 neutrons, and 4 alectrons. What is the mass number of this atom? a.4 b.5 c.8 d.9​

Sagot :

Answer:

D. 9

Explanation:

Atomic weight and mass number are the same.

Answer:

9

Mass number of beryllium =4+5=9.