A block of wood is floating in water at 0^oC. The temperature of water is slowly raised from 0^oC to 10^oC. With the rise in temperature the volume of block ZV above water level will

Fraction of wooden block immersed at 0^oC,

$\frac{{\mathrm{V}}_1}{{\mathrm{V}}_0}=\frac{{\left({\mathrm{\rho }}_{\text{wood }}\right)}_{0^{\circ }\mathrm{C}}}{{\left({\mathrm{\rho }}_{{\mathrm{H}}_2\mathrm{O}}\right)}_{0^{\circ }\mathrm{C}}}$

${\mathrm{f}}_1=\frac{{\mathrm{V}}_0-{\mathrm{V}}_1}{{\mathrm{V}}_0}=\frac{{\left({\mathrm{\rho }}_{{\mathrm{H}}_2\mathrm{O}}\right)}_{0^{\circ }\mathrm{C}}-{\left({\mathrm{\rho }}_{\mathrm{wood}}\right)}_{0^{\circ }\mathrm{C}}}{{\left({\mathrm{\rho }}_{{\mathrm{H}}_2\mathrm{O}}\right)}_{0^{\circ }\mathrm{C}}}$

$\begin{array}{l}{\mathrm{V}}_1-\text{ Volume of wood immersed in water at }{0}^{\circ }\mathrm{C}\\ {\mathrm{V}}_0-\text{ Volume of wood }\end{array}$

${\left({\mathrm{\rho }}_{\text{wood }}\right)}_{0^{\circ }\mathrm{C}}-\text{ Density of wood at }{0}^{\circ }\mathrm{C}$

When the temperature is raised to 10^oC, the volume of wood immersed in water changes to V₂.

$\begin{array}{l}\frac{{\mathrm{V}}_2}{{\mathrm{V}}_0}=\frac{{\left({\mathrm{\rho }}_{\text{wood }}\right)}_{{10}^{\circ }\mathrm{C}}}{{\left({\mathrm{\rho }}_{{\mathrm{H}}_2\mathrm{O}}\right)}_{{10}^{\circ }\mathrm{C}}}\\ {\mathrm{f}}_2=\frac{{\mathrm{V}}_0-{\mathrm{V}}_2}{{\mathrm{V}}_0}=\frac{{\left({\mathrm{\rho }}_{{\mathrm{H}}_2\mathrm{O}}\right)}_{{10}^{\circ }\mathrm{C}}-{\left({\mathrm{\rho }}_{\mathrm{wood}}\right)}_{{10}^{\circ }\mathrm{C}}}{{\left({\mathrm{\rho }}_{{\mathrm{H}}_2\mathrm{O}}\right)}_{{10}^{\circ }\mathrm{C}}}\end{array}$

From 0^oC to 4^oC, the density of water increases, and from 4^oC to l0oc the density of water decreases.
But for wood density decreases as temperature increases.
The volume of block above water level will first increase and then decrease.