Select the incorrect statement

$\left(1\right) {\mathrm{Mg}}_2{\mathrm{C}}_3+{\mathrm{H}}_2\mathrm{O}⟶\mathrm{Mg}(\mathrm{OH}{)}_2+{\mathrm{H}}_3\mathrm{C}-\underset{\mathrm{Propyne}}{\mathrm{C}\equiv \mathrm{CH}}$

${{\mathrm{C}}_3}^{4-}\text{ contains:}\underset{\mathrm{Proppide} \mathrm{ion}}{{\left[\mathrm{C}-\frac{\mathrm{\sigma }}{\mathrm{C}}\frac{\mathrm{\sigma }}{2\mathrm{\pi }}\mathrm{C}\right]}^{4-}}=2\mathrm{\sigma }\text{ and }2\mathrm{\pi }\text{ bonds }$

(2) Mg is more dense than Ca
(3) Fact
(4) Stability of peroxides and superoxides of alkali metals and stability of oxides and peroxides (since no superoxide in 2nd group) of 2nd group increases down the group. Increases in stability is due to stabilization of large anions by large cations, increases their lattice energy.
Lattice energy $\propto$ comparable size of cations and anions