  We explore the detection possibility of light pseudoscalar Higgs boson in the
next-to-minimal supersymmetric Standard Model(NMSSM) at the LHC with the center
of mass energy, $\sqrt{S}=13$ TeV. We focus on the parameter space which
provides one of the Higgs boson as the SM-like with a mass of 125 GeV and some
of the non-SM-like Higgs bosons can be light having suppressed couplings with
fermions and gauge bosons due to their singlet nature. It is observed that for
certain region of model parameter space, the singlet like light pseudoscalar
can decay to di-photon($\gamma\gamma$) channel with a substantial branching
ratio. In this study, we consider this di-photon signal of light pseudoscalar
Higgs boson producing it through the chargino-neutralino production and the
subsequent decay of neutralino. We consider signal consisting of two photons
plus missing energy along with a lepton from the chargino decay. Performing a
detailed simulation of the signal and backgrounds including detector effects,
we present results for a few benchmark points corresponding to the pseudoscalar
Higgs boson mass in the range 60 -100 GeV. Our studies indicate that some of
the benchmark points in the parameter space can be probed with a reasonable
significance for 100 fb$^{-1}$ integrated luminosity. We also conclude that
exploiting this channel it is possible to distinguish the NMSSM from the other
supersymmetric models.
