  We present the results obtained from our campaign to characterize the
intra-night-optical variability properties of blazars detected by the {\it
Fermi} Large Area Telescope. This involves R-band monitoring observations of a
sample of 18 blazars, that includes five flat-spectrum radio quasars (FSRQs)
and thirteen BL Lac objects (BL Lacs) covering the redshift range z =
0.085$-$1.184. Our observations, carried out using the 1.3 m J.C. Bhattacharya
Telescope cover a total of 40 nights ($\sim$200 hrs) between the period 2016
December and 2020 March. We characterized variability using the power enhanced
$F-$test. We found a duty cycle (DC) of the variability of about 11\% for FSRQs
and 12\% for BL Lacs. Dividing the sample into different sub-classes based on
the position of the synchrotron peak in their broadband spectral energy
distribution (SED), we found DC of $\sim$16\%, $\sim$10\% and $\sim$7\% for
low-synchrotron peaked (LSP), intermediate synchrotron peaked (ISP) and high
synchrotron peaked (HSP) blazars. Such high DC of variability in LSP blazars
could be understood in the context of the R-band tracing the falling part
(contributed by high energy electrons) of the synchrotron component of the
broadband SED. Also, the R-band tracing the rising synchrotron part (produced
by low energy electrons) in the case of ISP and HSP blazars, could cause lesser
variability in them. Thus, the observed high DC of variability in LSP blazars
relative to ISP and HSP blazars is in accordance with the leptonic model of
emission from blazar jets.
