Voluntary muscles are contained in the ___.
\( \frac{3}{12} \) of \(\frac{\left(\frac{2}{5}+\frac{4}{15}\right)}{\left(\frac{2}{5}-\frac{2}{5}\right)}\)=?
\( \frac{5}{7} \)
\( \frac{5}{6} \)
\( \frac{6}{5} \)
\( \frac{2}{6} \)
An element of atomic number 16 will belong to the ______ period of the periodic table.