Question

What is the mass defect for oxygen ${}_8{O}^{16}$ whose nuclear mass is 15.995 amu?

• A. 0.246 amu
• B. 0.137 amu
• C. 0.185 amu
• D. 0.225 amu

Answer 1

Answer: (B)

0.137 amu

$\begin{array}{cc}\text{Mass of}{}_8{O}^{16}=15.995amu& \\ \text{Mass of}1\text{proton}=& 1.0073\text{annu}\\ \text{Mass of}8\text{proton}=& 8\times 1.0073\\ & =8.0584amu\end{array}$

$\begin{array}{cc}\text{Mass of}1\text{neutron:}& 1.0087amu\\ \text{Mass of}8\text{neutron}& =8\times 1.0087\\ & =8.0696am4\\ \text{Mass of}1\text{electron}=& 0.000548amu\\ \text{Mass of}8\text{electron}& =8\times 0.000548\\ & =0.0044amu\end{array}$

$\text{Mass defect = Theoritical mass - calculated mass}$

$\begin{array}{c}\text{Mass of neutron + mass of proton+mass of electron}\end{array}$

$\begin{array}{c}8.0584+8.0696+0.004-15.995\\ 16.1324-15.995\\ 0.1374amu\end{array}$