# The percentage of oxygen in NaOH is

$\begin{array}{1 1}(a)\;1& (b)\;8 \\(c)\;16&(d)\;40\end{array}$

40g of NaOH contains 16g of oxygen
$\therefore$ % of oxygen =$\large\frac{16}{40}$$\times 100=40\%$
Hence (d) is the correct option.