What are $X$ and $Y$ respectively in the following reactions?

A metal ( $M$ ), crystallises in fcc lattice with edge length of $4.242 \mathop {\rm{A}}\limits^{\rm{o}}$. What is the radius of $M$ atom (in $\mathop {\rm{A}}\limits^{\rm{o}}$ )?

A solid mixture weighing 5 g contains equal number of moles of $\mathrm{Na}_2 \mathrm{CO}_3$ and NaHCO . This solid mixture was dissolved in 1 L of water. What is the volume (in mL ) of 0.1 M HCl required to completely react with this 1 L mixture solution?

At 298 K the equilibrium constant for the reaction $M(s)+2 \mathrm{Ag}^{+}(a q) \longrightarrow M^{2+}(a q)+2 \mathrm{Ag}(s)$ is $10^{15}$. What is the $E_{\text {cell }}^{\ominus}$ (in V) for this reaction?

$$ \left(\frac{2.303 R T}{F}\right)=0.06 \mathrm{~V} $$