Calculate the number of moles of acid in 200 cm3 of a 1.5 mol dm⁻³ solution.

Given volume is $200 \text{ cm}^3$.
Since $1 \text{ dm}^3 = 1000 \text{ cm}^3$, we convert the volume:

$$\text{Volume (in dm}^3) = \frac{200 \text{ cm}^3}{1000 \text{ cm}^3/\text{dm}^3} = 0.2 \text{ dm}^3$$

$$\text{Moles} = \text{Concentration} \times \text{Volume}$$

Given concentration is $1.5 \text{ mol dm}^{-3}$.

$$\text{Moles} = 1.5 \text{ mol dm}^{-3} \times 0.2 \text{ dm}^3$$ $$\text{Moles} = 0.3 \text{ mol}$$

The number of moles of acid present is $0.3 \text{ mol}$.