Take these standard potentials in acidic solution: $\mathrm{Ce}{}^{4+}/\mathrm{Ce}{}^{3+}$ = +1.61 V, $\mathrm{Fe}{}^{3+}/\mathrm{Fe}{}^{2+}$ = +0.77 V, $\mathrm{H}{}^{+}/\mathrm{H}{}_2$ = 0.00 V, $\mathrm{Eu}{}^{3+}/\mathrm{Eu}{}^{2+}$ = $-0.35$ V, $\mathrm{Yb}{}^{3+}/\mathrm{Yb}{}^{2+}$ = $-1.05$ V. Which reactions are spontaneous under standard conditions?

1. A$\mathrm{Ce}{}^{4+}$ oxidises $\mathrm{Eu}{}^{2+}$ to $\mathrm{Eu}{}^{3+}$
2. B$\mathrm{Eu}{}^{2+}$ reduces $\mathrm{H}{}^{+}$ to $\mathrm{H}{}_2$
3. C$\mathrm{Yb}{}^{3+}$ oxidises $\mathrm{Eu}{}^{2+}$ to $\mathrm{Eu}{}^{3+}$
4. D$\mathrm{Ce}{}^{4+}$ oxidises $\mathrm{Fe}{}^{2+}$ to $\mathrm{Fe}{}^{3+}$