What is the percentage by mass of oxygen in NaOH ? (Atomic mass of $\mathrm{Na}=23 \mathrm{u}, \mathrm{O}=16…

What is the percentage by mass of oxygen in NaOH ? (Atomic mass of $\mathrm{Na}=23 \mathrm{u}, \mathrm{O}=16 \mathrm{u}, \mathrm{H}=1 \mathrm{u}$ )
  1. 16
  2. 20
  3. 40
  4. 60

Solution

$\begin{aligned} \% \mathrm{O} \text { by mass } & =\frac{\text { Atomic weight of oxygen }}{\text { Molecular weight of } \mathrm{NaOH}} \times 100 \\ \therefore \quad & =\frac{16}{40} \times 100=40 \%\end{aligned}$

Asked in: MHT CET 2024 (15 May Shift 1)

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