  In the context of a nonuniversal and anomaly free $U(1)_{X}$ extension of the
standard model, we examine the decay of a $750$GeV scalar singlet state,
$\xi_{\chi}$, as a possible explanation of the observed diphoton excess
announced by the ATLAS and CMS collaborations at CERN-LHC collider. One-loop
decay to photons is allowed through three heavy singlet quarks and one charged
Higgs boson into the loop. We obtain, for different width approximations and
for masses of the exotic singlet quarks in the region $[900,\,3000]$ GeV, a
production cross section $\sigma(pp\to\xi_{\chi}\to\gamma\gamma)$ compatible
with ATLAS and CMS collaborations data. We also include another scalar singlet,
$\sigma$, as a dark matter candidate that may couple with the 750 GeV scalar at
tree level with production cross sections in agreement with ATLAS and CMS.
