\(a.\)
\(n_{Na_2CO_3}=\dfrac{10.6}{106}=0.1\left(mol\right)\)
\(n_{Na}=0.1\cdot2=0.2\left(mol\right)\)
\(\Rightarrow\%Na=\dfrac{0.2\cdot23}{10.6}\cdot100\%=43.39\%\)
\(n_C=0.2\left(mol\right)\)
\(\Rightarrow\%C=\dfrac{0.1\cdot12}{10.6}\cdot100\%=11.32\%\)
\(n_O=0.2\cdot3=0.6\left(mol\right)\)
\(\Rightarrow\%O=\dfrac{0.6\cdot16}{10.6}\cdot100\%=45.29\%\)
\(b.\)
\(n_{Ca_3\left(PO_4\right)_2}=\dfrac{620}{310}=2\left(mol\right)\)
\(n_{Ca}=3\cdot2=6\left(mol\right)\)
\(\Rightarrow\%Ca=\dfrac{6\cdot40}{620}\cdot100\%=38.71\%\)
\(n_P=2\cdot2=4\left(mol\right)\)
\(\Rightarrow\%P=\dfrac{4\cdot31}{620}\cdot100\%=20\%\)
\(n_O=2\cdot8=16\left(mol\right)\)
\(\Rightarrow\%O=\dfrac{16\cdot16}{620}\cdot100\%=41.29\%\)
