(i) Ratio of calcium, carbon, and oxygen = \(10: 3: 12\)
As \(10 + 3 +12 = 25\),
Therefore, percentage of carbon = \(\frac{3}{25}\times100=12\%\)
(ii) Let the weight of the stick be \(x\) \(g\).
\(12 \%\) of \(x\) = \(3\)
\(\frac{12}{100}\times x=3\)
\(x= 3\times \frac{100}{12}=25\;g\)