Answer
The percentage deviation is $~~0.83~\%$
Work Step by Step
We can find the percentage deviation for $^{120}Sn$:
$\frac{M_{app}-M}{M}~\times 100\%$
$= \frac{A~m_p-119.902 197~u}{119.902 197~u}~\times 100\%$
$= \frac{(120)(1.673\times 10^{-27}~kg)-(119.902 197)(1.660538782\times 10^{-27}~kg)}{(119.902 197)(1.660538782\times 10^{-27}~kg)}~\times 100\%$
$= 0.83~\%$
The percentage deviation is $~~0.83~\%$
