The immersed portion of a piece of pure ice floating in water is:

According to the law of floatation, the fraction of the volume of a floating body that is submerged in a fluid ($f_{\text{sub}}$) is equal to the ratio of the density of the floating body (${\rho }_{\text{body}}$) to the density of the fluid (${\rho }_{\text{fluid}}$):
$$f_{\text{sub}}=\frac{V_{\text{sub}}}{V_{\text{total}}}=\frac{{\rho }_{\text{ice}}}{{\rho }_{\text{water}}}$$

The density of pure ice is approximately $0.917{\text{g/cm}}^3$ and the density of pure water is $1.0{\text{g/cm}}^3$.

$$f_{\text{sub}}\approx \frac{0.917}{1.0}\approx 0.917\approx 91.7\%$$

Approximating this value to standard fractional choices yields $\frac{9}{10}$ (since $\frac{9}{10}=0.90$ or $90\%$, which matches the closest standard textbook representation for general physics options).