The concentration of 1 L of $\mathrm{CaCO}_3$ solution is 1000 ppm . What is its concentration in mol $\mathrm{L}^{-1}$ ?

$$ (\mathrm{Ca}=40 \mathrm{u}, \mathrm{O}=16 \mathrm{u}, \mathrm{C}=12 \mathrm{u}) $$

The $E^{-}$of $M\left|M^{2+} \| \mathrm{Cu}^{2+}\right| \mathrm{Cu}$ is 0.3 V .

At what concentration of $\mathrm{Cu}^{2+}\left(\mathrm{in} \mathrm{mol} \mathrm{L} \mathrm{L}^{-1}\right)$, the $\mathrm{E}_{\mathrm{cel}}$ value becomes zero ? $\left(\frac{2.303 R T}{F}=0.06\right)$

(Conc. of $\mathrm{M}^{2+}=0.1 \mathrm{M}$ )