  The India-based Neutrino Observatory (INO) is a project aimed at building a
large underground laboratory to explore the Earth's mater effects on the
atmospheric neutrinos in multi-GeV range. INO will host a 50 kton magnetized
iron calorimeter detector (ICAL) in which Resistive Plate Chambers(RPCs) will
be the active detector elements. In ICAL, 28,800 glass RPCs of 2 m $\times$ 2 m
size will be operated in the avalanche mode. A small variation in the
compositions of ionizing gaseous medium in the RPC affects its performance.
Study of the charge distribution of the RPC at different gas compositions is
necessary to optimize the gas mixture.
  An RPC made with glass plates of dimension 30 cm $\times$ 30 cm was operated
in avalanche mode with a gas mixture of $C_2H_2F_4$/$iC_4H_{10}$/$SF_6$. We
have studied the performance of these RPCs at the same ambient conditions. The
percentages of the $iC_4H_{10}$ or $SF_6$ were varied and its effect on the
performance of RPC were studied. The study of the charge distribution and time
resolution of the RPC signals at different gas compositions is presented in
this paper.
