Let $V$ be the volume $g$ water. displaced by ice due to mass.

$V=$ volume og water displaced.

$m_1=$ mass of ice

$m_2=$ mass of iron pitce,

$\rho_1=$ density of water,

$\rho_2=$ density of iron piece.

Now, $v=\frac{\left(m_1+m_2\right)}{\rho_1} \quad[$ before melting $]$.

And, $\quad V^{\prime}=\frac{m_1}{\rho_1}+\frac{m_2}{\rho_2} \quad[$ after melting $]$.

Since $\rho_2 > \rho_1$. So, $\quad \frac{m_2}{\rho_2} < \frac{m_2}{\rho_1}$.

Thus, $\quad v > V^{\prime}$

So, when the whole ice melts, the volume of water decreases.