Answer
$11 g/cm^{3}$
Work Step by Step
Volume = $0.50 cm\times1.55 cm\times25.00cm$
Mass = 220.9 g
Density = $\frac{Mass}{Volume} = \frac{220.9g}{0.50 cm\times1.55 cm\times25.00cm} = \frac{220.9 g}{19.375cm^{3}} = 11 \frac{g}{cm^{3}}$ (rounded at the end to 2 significant figures as 0.50 contains only 2 significant figures).
