To find the density of the unknown metal, we use the formula \( d = \frac{m}{v} \), where \( d \) is density, \( m \) is mass, and \( v \) is volume.
Given:
- Mass (\( m \)) = 17.8 g
- Volume (\( v \)) = 2 cm³
Now, we can calculate the density:
\[ d = \frac{17.8 , \text{g}}{2 , \text{cm}^3} = 8.9 , \text{g/cm}^3 \]
Now, we can compare this calculated density (8.9 g/cm³) with the known densities of the metals listed:
- Chromium: ~7.19 g/cm³
- Platinum: ~21.45 g/cm³
- Lead: ~11.34 g/cm³
- Silver: ~10.49 g/cm³
- Cobalt: ~8.90 g/cm³
Since the computed density of 8.9 g/cm³ matches closely with the density of Cobalt, the unknown metal is Cobalt.