a)\(m_{Na}=11\cdot\left(1,6726\cdot10^{-27}+9,1094\cdot10^{-31}\right)+12\cdot1,6748\cdot10^{-27}=18,3986\cdot10^{-27}+100,2034\cdot10^{-31}+20,0976\cdot10^{-27}=\left(183986+100,2034+200976\right)\cdot10^{-31}=385062,2034\cdot10^{-31}\sim38,5\cdot10^{-27}kg\sim23,193u\)Các phần khác tương tự.
\(m_{ntu}=m_p+m_n+m_e\)