The mass of the nucleus is 17 amu.
Explanation
Given :
Number of Protons = 8
Number of Neutrons = 9
To Find :
Mass of the nucleus = ?
Solution :
The mass of the nucleus Mass= p+n
Where
p= protons in the atom
n= neutrons in the atom
So, substituting the values
Mass= 8+9
Mass= 17 amu