Em tham khảo nha:
\(\begin{array}{l}
a)\\
{}_{26}^{56}Fe\\
b)\\
{p_{Ca}} = {n_{Ca}} = 20\\
{A_{Ca}} = 20 + 20 = 40\\
\Rightarrow {}_{20}^{40}Ca\\
c)\\
{A_{Na}} = 11 + 12 = 23 \Rightarrow {}_{11}^{23}Na\\
d)\\
{p_S} + {n_S} = 32 \Rightarrow 2{p_S} = 32 \Rightarrow {p_S} = 16\\
\Rightarrow {}_{16}^{32}S
\end{array}\)