Which of the following is a reaction of combination?

$3\mathrm{Mg}+{\mathrm{N}}_2\to {\mathrm{Mg}}_3{\mathrm{N}}_2$ This is combination reaction

$\mathrm{Ca}\left(\mathrm{s}\right)+{\mathrm{V}}_2{\mathrm{O}}_5\left(\mathrm{s}\right)\to 2\mathrm{V}\left(\mathrm{s}\right)+5\mathrm{CaO}\left(\mathrm{s}\right)$ This is Redox reaction

$2{\mathrm{KClO}}_3\left(\mathrm{s}\right)\stackrel{∆}{\to }2\mathrm{KCl}\left(\mathrm{s}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)$ This is decomposition reaction

${\mathrm{P}}_4\left(\mathrm{s}\right)+3{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{PH}}_3 +3{\mathrm{H}}_2{\mathrm{PO}}_2^{-}$ This reaction is disproportination reaction