First, we need to calculate the volume of the ice block using the formula for the volume of a rectangular prism:
\[ \text{Volume} = \text{height} \times \text{length} \times \text{width} = 2 , \text{cm} \times 2 , \text{cm} \times 5 , \text{cm} = 20 , \text{cm}^3. \]
Next, we can calculate the density of the ice block by using its mass and volume:
\[ \text{Density} = \frac{\text{mass}}{\text{volume}} = \frac{18.4 , \text{g}}{20 , \text{cm}^3} = 0.92 , \text{g/cm}^3. \]
Since the density of the ice block (0.92 g/cm³) is less than the density of water (1 g/cm³), the ice block will float in the water. An object will float if it is less dense than the fluid it is placed in. Therefore, we conclude that the ice block will float when dropped into the water.