Three sols are tested. Sol X is coagulated by $\mathrm{Na}{}_3\mathrm{PO}{}_4$ at a lower concentration than by $\mathrm{Na}{}_2\mathrm{SO}{}_4$, which in turn needs a lower concentration than $\mathrm{NaCl}$. Sols Y and Z are each coagulated at lower concentrations by $\mathrm{AlCl}{}_3$ than by $\mathrm{BaCl}{}_2$, and by $\mathrm{BaCl}{}_2$ than by $\mathrm{NaCl}$. When sols are mixed in suitable proportions, which statement is correct?

1. AX coagulates with Y and with Z on mixing, but Y and Z do not coagulate each other
2. BY coagulates with Z, but X coagulates with neither
3. CX, Y and Z coagulate one another on pairwise mixing
4. DX coagulates only with Y, and Z coagulates with neither